Blowing Agents: 9 Types, Mechanisms, Dosage and Selection

Blowing agents are substances that release or become a gas inside a polymer melt and expand it into a cellular foam; the 9 types split into 5 chemical agents, which generate gas by decomposing or reacting, and 4 physical agents, which are already a gas or a volatile liquid. They make up 0.05 to 20 wt% of a finished foamed plastic, and each type works in a narrow temperature window, so which one fits which polymer and process?

Blowing agents are one of the 43 families of plastic additives and belong to the functional group that gives a polymer a property it does not have on its own, alongside flame retardants, antimicrobials and barrier additives. The 0.05 to 20 wt% range comes from the review by John Hahladakis and colleagues at the University of Leeds (Journal of Hazardous Materials, 2018), as tabulated by Chea and co-workers in 2025.

What follows runs in the order a formulator meets the subject: the definition and the foaming-agent synonym, what foaming changes in a part, the gas-generation mechanism and its heat balance, the 9 types with their decomposition temperatures and gas yields, the chemical-or-physical decision, the polymer and process fit, dosage and masterbatch let-down, formulation interactions, test methods, the F-gas, AIM Act and food-contact rules, the producers, and the 14 substances.

Every figure on this page is checked against primary sources; see our methodology and fact-checking process.

The 9 types differ in how the gas appears, at what temperature it appears, how much gas each gram delivers and whether the reaction heats or cools the melt.

Table T1. The 9 types of blowing agents for plastics at a glance.

Decomposition and boiling values are representative grade or literature values, not specifications. Data for TSH, TSSC and 5-phenyltetrazole are not published in a primary source we could verify.

What Is a Blowing Agent in Plastics?#

A blowing agent is a substance that decomposes, reacts or vaporises on heating and releases a gas that forms a cellular structure inside a polymer. The gas is rarely a single species: azodicarbonamide delivers nitrogen, carbon monoxide, carbon dioxide and ammonia, while a bicarbonate system delivers carbon dioxide and water vapour. The agent reaches the melt as a powder, a pellet concentrate, a compressed gas or a volatile liquid.

Which ways of putting cells into a plastic therefore do not involve a blowing agent? Mechanical frothing whips air into a plastisol or a latex before it is gelled, so the gas is entrained rather than generated. Hollow fillers such as glass microspheres in plastics lower density by occupying volume with a pre-formed void, which is a filler function rather than a foaming one.

Blowing agent vs foaming agent: is there a difference?#

In plastics the two words mean the same thing: a foaming agent and a blowing agent are both substances that create the gas that expands a melt into a foam. The split is one of register, since supplier data sheets from Avient, Tramaco and Tosaf say foaming agent while the academic and regulatory texts say blowing agent.

The abbreviations follow the same divide. CFA means chemical foaming agent and CBA chemical blowing agent, for the identical class; PBA means physical blowing agent; LBA, liquid blowing agent, is Honeywell's term for HCFO-1233zd(E); and AC foaming agent means azodicarbonamide in Chinese and Indian trade usage. Outside plastics, a foaming agent in soap, cosmetics or oilfield chemistry is a surfactant that traps air in a liquid.

What does a blowing agent change in the finished part?#

A blowing agent changes 5 things at once: it lowers density and part weight, it cuts the amount of polymer used, it adds thermal insulation, it removes sink marks and warpage, and it turns a rigid material into a cushioning one. Each effect carries a measured value in at least one published case.

• Density and weight. Expanded polystyrene reaches 11 to 32 kg/m3 and is 95 to 98 % air, and EVA foam lands at 0.15 to 0.25 g/cm3 on the chemical route and 0.13 g/cm3 with nitrogen.
• Material cost. Avient reports 10 to 20 % less plastic with its Hydrocerol grades, including a 20 % weight reduction on an instrument-panel case, both supplier claims.
• Thermal insulation. Extruded polystyrene board reaches 0.029 to 0.039 W/(m·K), and rigid polyurethane blown with fourth-generation agents reaches 17.1 to 21.1 mW/(m·K).
• Sink marks and warpage. A small gas volume holds pressure inside a thick section while it cools, which is why endothermic grades are dosed into mouldings that would otherwise sink.
• Cushioning. A closed-cell structure converts a rigid wall into an energy-absorbing one in footwear, weather strip and packaging.

How Do Blowing Agents Work? Gas Generation, Nucleation and Cell Growth#

Foaming happens in 3 steps: the blowing agent releases or becomes gas, the gas nucleates into bubbles at seed points in the melt, and the bubbles grow until the melt freezes or the pressure equalises. Step one is chemistry for a chemical agent and physics for a physical one.

Nucleation decides how many cells form, and therefore how small they are at a given density. A supersaturated melt drops bubbles out of solution at solid seed points, which is why an undissolved bicarbonate particle doubles as a nucleant, and the same seeding logic drives crystallization, which is covered on nucleating agents. Cells in microcellular moulding are typically 0.1 to 100 µm across, and gas counter-pressure cut cell size by 45 % to 20.9 µm in one polycarbonate study.

Cell growth is then a contest between gas pressure and melt strength. A melt that cannot hold the gas needs melt strength enhancers or a long-chain-branched grade, otherwise the cells coalesce and the foam collapses.

Exothermic or endothermic: why the heat balance decides the cell structure#

Exothermic blowing agents release heat as they decompose, which speeds the reaction and can overheat a thick section, while endothermic agents absorb heat, which cools the melt, gives finer cells and shortens the cooling step. Azodicarbonamide releases 1.36 kJ/g over a 160 to 230 °C calorimetry scan and has an activation energy of 182 kJ/mol, so once decomposition starts in a thick wall it feeds itself and can scorch the core.

Sodium bicarbonate does the opposite, decomposing to sodium carbonate, water and carbon dioxide while absorbing heat over roughly 120 to 200 °C. Sadik, Pillon, Carrot and Reglero Ruiz (Thermochimica Acta, 2018) did the reference calorimetry on citric acid and bicarbonate systems. The trade-off is yield.

Table T3. Exothermic against endothermic chemical blowing agents.

How activators (kickers) lower the decomposition temperature#

Activators, called kickers in the trade, are metal oxides, metal soaps and amides that lower the decomposition temperature of azodicarbonamide from about 200-209 °C to 140-165 °C so it fits the processing window of PVC, EVA and polyethylene. Three activator classes cover almost every commercial system.

• Metal oxides. Zinc oxide is the standard kicker, and ECHA holds a registered reaction mass of C,C'-azodi(formamide) and zinc oxide under EC number 907-545-1, an activated ADC sold as a single substance.
• Metal soaps. Zinc stearate acts as kicker and lubricant at once, which is why it appears in PVC recipes that already need external lubrication.
• Amides and phosphates. Urea is the classic organic activator, and in one 2024 study of rotational polyethylene foaming an ammonium dihydrogen phosphate surface treatment lowered the ADC onset from about 210 °C to about 180 °C.

Activation costs gas: Eiwa's DW#6 decomposes at 165 °C and still gives 210 mL/g, while FE-788 decomposes at 140 °C and gives 135 mL/g. Zinc oxide, zinc stearate and urea systems are compared on blowing agent activators (kickers).

9 Types of Blowing Agents for Plastics#

The 9 types of blowing agents for plastics fall into 5 chemical types, which make gas by decomposing or reacting (azo compounds, sulfonyl hydrazides, sulfonyl semicarbazides and tetrazoles, endothermic carbonates, and water in polyurethane), and 4 physical types, which are already gas or volatile liquid (inert gases, hydrocarbons and oxygenates, fluorinated agents, and expandable microspheres).

Chemical blowing agents: 5 types that release gas by decomposition or reaction#

Chemical blowing agents are solids or liquids compounded into the polymer that generate gas by decomposing or reacting on heating; the group has 5 types, and the selection variable for all of them is the decomposition temperature, which must sit above the melting point of the polymer and below the temperature at which the polymer degrades. The five are azo compounds, sulfonyl hydrazides, sulfonyl semicarbazides and tetrazoles, endothermic carbonates, and the reactive in-situ water system used in polyurethane.

Chemical agents need no gas-dosing hardware, which is why they dominate extrusion and injection moulding. Where the regulatory status of azodicarbonamide rules it out, the ADC-free routes are set out on azodicarbonamide alternatives.

Table T2. Decomposition temperature and gas yield of the chemical blowing agents.

Unverified cells mean the value is not published in a primary source we could verify, not that it does not exist. Grade values are representative, not specifications.

1. Azo compounds: azodicarbonamide (ADC) and activated ADC#

Azodicarbonamide is the workhorse chemical blowing agent: a yellow-to-orange azo powder that decomposes at about 200-209 °C in standard grades and releases 200-220 mL of gas per gram, mostly nitrogen with carbon monoxide, carbon dioxide and ammonia. Its CAS number is 123-77-3 and its EC number 204-650-8, its density is 1.65 g/cm3 at 20 °C, and decomposition is exothermic at 1.36 kJ/g with an activation energy of 182 kJ/mol. It leaves biurea, urazole and cyanuric acid in the part, with semicarbazide as a secondary product.

Activated grades carrying zinc oxide, zinc stearate or urea move the onset to 140 to 165 °C, which is what makes ADC usable in PVC plastisol, EVA and polyethylene. It has been on the REACH Candidate List since 19 December 2012 for respiratory sensitising properties, and 21 CFR 178.3010 allows it at up to 5 % of the finished foamed polyethylene.

2. Sulfonyl hydrazides: OBSH and TSH#

Sulfonyl hydrazides are lower-temperature exothermic blowing agents: OBSH decomposes at about 160-165 °C and releases 120-125 mL of nitrogen and water vapour per gram, which is too low for polyethylene extrusion but right for PVC plastisol, EVA and rubber-like sheet. OBSH, 4,4'-oxybis(benzenesulfonyl hydrazide), carries CAS 80-51-3, both sulfonyl hydrazide groups decompose, and the reaction is milder than that of ADC.

Non-staining residues keep OBSH in wallpaper, coated fabric and white plastisol. TSH (p-toluenesulfonyl hydrazide, CAS 1576-35-8) melts at 108 to 110 °C and carries the harmonised classification Self-react. D, H242, but its decomposition temperature and gas yield are not published in a primary source we could verify, so neither value is stated here.

3. Sulfonyl semicarbazides and tetrazoles: TSSC and 5-phenyltetrazole#

Sulfonyl semicarbazides and tetrazoles are the high-temperature chemical blowing agents, used where a polymer is processed above the azodicarbonamide window, for example when polybutylene terephthalate is foamed by extrusion. TSSC, p-toluenesulfonyl semicarbazide, carries CAS 10396-10-8 and releases nitrogen, carbon dioxide and ammonia. 5-Phenyltetrazole carries CAS 18039-42-4 and EC 241-950-8, has the formula C7H6N4 and a molar mass of 146.15 g/mol, and works by ring opening, which releases nitrogen. Jeong and co-workers used it to foam PBT by extrusion.

Neither substance has a decomposition temperature or gas yield published in a source we could verify, so this site states neither. No active REACH registration for TSSC was found on ECHA CHEM when checked on 22 September 2026, and 5-phenyltetrazole holds an intermediate-only registration.

4. Endothermic carbonates: sodium bicarbonate and citric acid#

Endothermic blowing agents are sodium bicarbonate systems, usually paired with citric acid, that absorb heat while releasing carbon dioxide and water over roughly 120 to 200 °C. Sodium bicarbonate carries CAS 144-55-8 and citric acid CAS 77-92-9, and with citric acid present an acid-base reaction releases carbon dioxide at a lower temperature than thermal decomposition alone. So yes, baking soda is a foaming agent in the plastics sense.

Three consequences follow from the heat balance: cells are finer and more uniform, cooling is shorter, and post-expansion is smaller. Bicarbonate also doubles as a nucleant for gas-injection foaming. Carbonic acid salts are FCM 21 and citric acid is FCM 139 in the EU Union list, while azodicarbonamide is absent from it.

5. Reactive in-situ systems: water and isocyanate in polyurethane#

In polyurethane the blowing agent can be water: it reacts with the isocyanate during the same exotherm that builds the polymer and releases carbon dioxide, which is why water-blown foam needs no separate gas at all. The reaction is part of the polymerisation, so there is no independent decomposition temperature to match.

Dosage is written in parts per hundred polyol: a flexible reference formulation runs water at 6 pphp with a silicone surfactant at 0.2 pphp, stannous octoate at 0.2 and PMDETA at 0.5, at an isocyanate index of 100. The isocyanate and the polyol are reactants that become the polymer, not additives dosed into a finished resin. Foam accounted for 67 % of polyurethane use in 2016, the largest single application of any blowing-agent chemistry.

Physical blowing agents: 4 types that expand without decomposing#

Physical blowing agents are gases or volatile liquids that are dissolved, injected or encapsulated in the melt and expand when the pressure drops or the temperature rises; the group has 4 types, they leave no chemical residue, and their selection variables are the boiling point, the solubility in the polymer and, for the fluorinated agents, the global warming potential. The four are inert gases, hydrocarbons and oxygenates, fluorinated agents, and expandable microspheres, which are the particle form of the same principle.

6. Inert gases: supercritical nitrogen and carbon dioxide#

Nitrogen and carbon dioxide are the cleanest blowing agents: dissolved in the melt as supercritical fluids, they leave no residue, have no global warming issue of their own and give the widest processing window of any type. The industrial form of the idea is MuCell, microcellular injection moulding with supercritical nitrogen as the standard gas and carbon dioxide as the alternative, invented in 1979 at MIT by J. E. Martini and F. A. Waldman under Nam P. Suh and a Trexel trademark since 2001.

The price is hardware: a gas-dosing unit, a modified screw and a pressurised feed. Carbon dioxide is FCM 307 in the EU Union list, so the inert-gas route is open for food-contact foam.

7. Hydrocarbons and oxygenates: pentane, cyclopentane, isobutane, methyl formate#

Hydrocarbons and oxygenates are the non-fluorinated volatile liquids: pentane boils at 36.1 °C and blows expandable polystyrene beads, cyclopentane boils at 49.2 °C and blows appliance insulation foam, and both sit outside the F-gas rules because neither is a fluorinated greenhouse gas. n-Pentane carries CAS 109-66-0 and cyclopentane CAS 287-92-3, and the oxygenate options for polyurethane are methyl formate and methylal.

Flammability is the trade-off, handled with plant engineering rather than with formulation, since pentane storage, bead maturation and appliance foaming lines all run as classified areas. n-Pentane is FCM 244 and isopentane FCM 143 in the EU Union list, neither with a specific migration limit, and 21 CFR 178.3010 permits both in polystyrene.

8. Fluorinated blowing agents: HFCs, HFOs and HCFOs#

Fluorinated blowing agents are the insulation specialists: the fourth-generation HCFO-1233zd(E) and HFO-1336mzz(Z) have global warming potentials of 3.88 and 2.08 against 1030 for the HFC-245fa they replace, and they give rigid polyurethane a thermal conductivity of 17.1 to 21.1 mW/(m·K). HCFO-1233zd(E) carries CAS 102687-65-0, and HFO-1336mzz(Z) carries CAS 692-49-9, EC 700-651-7, formula C4H2F6 and molar mass 164.05 g/mol, sold as Opteon 1100.

Performance and regulation pull in opposite directions. In one comparison of effective rate in polyurethane the ranking runs HFC-245fa, then HFO-1336mzz(Z), HFC-365mfc, HCFO-1233zd(E) and HCFC-141b, across a band from about 50 to almost 90 %. Foams containing fluorinated greenhouse gases, including the fourth-generation HFOs, are banned in the European Union from 1 January 2033 unless required to meet safety requirements.

9. Expandable microspheres#

Expandable microspheres are the particle form of a physical blowing agent: a hydrocarbon core sealed inside a thermoplastic shell that softens and inflates, expanding more than 40 times in volume without ever releasing its gas into the polymer. Shells are copolymers of vinylidene chloride, methyl methacrylate and acrylonitrile, and 0.2 to 0.4 wt% of divinylbenzene widens the stable expansion range by about 30 °C. Expancel 920 DU 40 has a median particle size of 10 to 16 µm and an expanded density of about 17 kg/m3.

The processing limit is the shell, not the core: above 220 °C the spheres shrink or rupture, so barrel profiles stay below about 180 to 190 °C. Because the gas never escapes the shell, the closed-cell structure survives shear, which makes microspheres the specialist choice for TPE, shoe soles, artificial leather and weather strip.

Chemical or Physical Blowing Agent: How to Decide#

Choose a chemical blowing agent when the foam has to be made on existing extrusion or injection equipment, and a physical blowing agent when density, cell size or residue matter more than capital cost. The EVA case is the cleanest worked comparison available: the azodicarbonamide route reaches 0.15 to 0.25 g/cm3 in a 170 to 190 °C window, while nitrogen at 15 MPa reaches 0.13 g/cm3 across 80 to 180 °C.

A chemical agent leaves its decomposition products in the part and a physical agent leaves nothing behind, yet regulatory pressure sits almost entirely on the fluorinated physical agents.

Table T4. Chemical against physical blowing agents, by decision factor.

Capital cost decides most projects: microcellular moulding delivered a 17 to 32 % weight reduction in the polycarbonate case study but required a licensed gas-injection system, while 1.5 wt% of expandable microspheres delivered a 5.75 % density reduction in HDPE with no equipment change. The whole additive package of a foam is on additives for plastic foams.

Which Blowing Agent Suits Each Polymer and Process?#

The blowing agent is chosen by matching its gas-release temperature to the processing window of the polymer: PVC plastisol fuses far below the standard azodicarbonamide window, polyethylene extrudes near it, and polybutylene terephthalate is processed above it. The second criterion, whether the plant can handle a gas, only decides between routes once the temperature question is settled. Every polymer has its own formulation guide under additives by polymer.

Table T5. Blowing agent by polymer and process.

Blowing agents for PVC foam#

PVC foam is the classic azodicarbonamide application: cushion vinyl flooring, wallpaper and artificial leather all use activated grades that decompose at 140 to 165 °C, inside the fusion range of a plastisol. A standard grade at 200 to 209 °C would never decompose in a spread-coating line, which is why the zinc kicker is not optional here. OBSH takes the applications where the yellow residue of an azo agent would show, and endothermic systems take the rigid foam core.

PVC foam is not peroxide-crosslinked in core applications, so melt strength comes from the resin and the plasticiser level. The 2005 EU food-contact suspension of azodicarbonamide does not touch flooring or wallpaper, but the SVHC listing does: residual ADC above 0.1 % w/w in an article triggers the REACH Article 33 duty and a SCIP notification, and no residual-level figure is published here because none is established in our sources. The rest of the PVC package is on additives for PVC.

Blowing agents for polyolefin foam (PE, PP and EVA)#

Crosslinked polyolefin foam is made by running a blowing agent and a crosslinking peroxide in the same formulation, so that the melt gains enough strength to hold the gas as the azodicarbonamide decomposes. A published EVA midsole laboratory formulation runs 1.35 phr of ADC with 2 phr of zinc oxide and 0.5 to 0.7 phr of BIPB, pressed at 165 to 190 °C, and BIPB gives a gel content of 78 % at 0.7 phr and 91 % at 1.2 phr. Peroxide and silane routes are compared on crosslinking agents for polymers.

Polypropylene behaves differently because it degrades by chain scission. In electron-beam crosslinked PP/POE foam, TMPTMA is used as a coagent at up to 8 phr, crosslinking peaks at 55 % at 15 kGy, and PP melt viscosity drops sharply above 2 kGy.

The US food-contact ceiling is 5 wt% of ADC in foamed polyethylene under 21 CFR 178.3010, a legal maximum rather than a formulation target. The wider package is on additives for polyethylene.

Blowing agents for polystyrene (EPS and XPS)#

Expandable polystyrene is blown with pentane impregnated into the bead, which is why finished EPS is 95 to 98 % air at a density of 11 to 32 kg/m3. The bead is pre-expanded with steam, matured, then moulded, while extruded polystyrene board has the gas injected into the extruder and reaches 0.029 to 0.039 W/(m·K), averaging near 0.035.

n-Pentane is FCM 244, isopentane FCM 143 and 1,1-difluoroethane FCM 131 in the EU Union list, and 21 CFR 178.3010 permits all three in polystyrene, with tetrachloroethylene at up to 0.3 % and toluene at up to 0.35 % as adjuvants. XPS was the first foam sector the F-gas Regulation reached: HFCs with a GWP of 150 or more have been banned in XPS since 1 January 2020. The polystyrene package is on additives for polystyrene.

Blowing agents for polyurethane and PIR insulation#

Polyurethane is the foam sector where blowing-agent choice is decided by climate rules rather than by chemistry: water, cyclopentane, HCFO-1233zd(E), HFO-1336mzz(Z), methyl formate and methylal all compete for the same insulation applications. Water is the cheapest and most widely used, at 6 pphp in the flexible reference formulation, but carbon dioxide diffuses out of a closed cell faster than a fluorinated vapour, so the best insulation values, 17.1 to 21.1 mW/(m·K), come from the physical agents.

Cyclopentane is the appliance answer in Europe, with zero ozone depletion potential and no exposure to the F-gas foam bans, at the cost of a flammable process. The fluorinated route buys the highest effective rate and pays with the 1 January 2033 EU ban and the US AIM Act limit in force since 1 January 2025. Cell stabilisation is covered on silicone surfactants for polyurethane foam, and the wider package is on additives for polyurethane.

Blowing agents for engineering thermoplastics#

Engineering thermoplastics are processed at 240 to 320 °C, far above the azodicarbonamide window, so they are foamed either with high-temperature organic agents such as 5-phenyltetrazole or with supercritical nitrogen and carbon dioxide. At those melt temperatures an azo agent has fully decomposed before the melt reaches the gate, and expandable microspheres rupture.

The organic option is narrow: 5-phenyltetrazole is the agent used for PBT extrusion foaming and TSSC is the other high-temperature choice, but neither has a verified published decomposition temperature. The physical option carries published numbers: in the microcellular polycarbonate case study, 2 % supercritical carbon dioxide at 290 °C melt and 80 °C mould gave a 17 to 32 % weight reduction.

How to select a blowing agent in 7 steps#

Select a blowing agent in 7 steps: set the density target, fix the polymer and its processing window, decide between chemical and physical, match the gas-release temperature, define the cell structure, screen the regulations, then set the dosage and run a trial. Each step removes candidates, and the order matters.

1. Set the density or weight-reduction target as a finished density in kg/m3 or g/cm3, or as a percentage of the unfoamed part weight.
2. Fix the polymer and its processing window, writing down the melt temperature range and the degradation temperature.
3. Choose chemical or physical from the equipment you have. A standard extruder limits the choice to a chemical agent or microspheres; a gas-dosing unit opens the physical route.
4. Match the decomposition or boiling temperature to that window. Standard ADC decomposes at 200 to 209 °C, bicarbonate systems over 120 to 200 °C, OBSH at 160 to 165 °C, and pentane boils at 36.1 °C. Add an activator only if the gap still needs closing.
5. Check the cell structure the application needs. Fine and closed calls for an endothermic grade, a nucleant or a physical route; coarse and cushioning tolerates an exothermic agent.
6. Screen the regulatory status against the EU Union list and 21 CFR for food contact, the F-gas Regulation and 40 CFR 84.54 for climate, and the REACH Candidate List for chemicals.
7. Set the dosage, convert it to masterbatch let-down and confirm by trial, because the only reliable expansion figure is the measured one.

Formulators should treat steps 2 and 6 as veto steps, since a temperature mismatch and a regulatory block each remove a candidate outright. The same framework applied to every additive family is on how to select plastic additives.

How Much Blowing Agent Is Needed? Dosage, Masterbatch and Weight Reduction#

Blowing agents make up 0.05 to 20 wt% of a finished foamed plastic, but the number a formulator works with is the dose of active agent: 1.35 phr of azodicarbonamide in an EVA midsole, 1.5 wt% of expandable microspheres in an HDPE moulding, or 2 % of supercritical carbon dioxide in a microcellular polycarbonate part. That range spans every foam from a nucleated injection moulding to an EPS bead that is almost all gas, and it describes the finished population rather than a recommendation.

Conversion between phr, wt% and ppm is set out on PHR (parts per hundred resin). Gas yield matters just as much: an agent delivering 120 mL/g needs almost twice the mass of one delivering 220 mL/g.

Table T6. Dosage by blowing agent type and host.

No verified dosage exists in our sources for OBSH, TSH, TSSC or 5-phenyltetrazole in plastics; ask the supplier for the grade data sheet.

The regulatory ceilings above are never formulation targets: the 5 wt% figure for azodicarbonamide is the maximum the United States permits in a food-contact article, and technical doses sit an order of magnitude below it. Weight reduction is the output rather than the input: 17 to 32 % in the microcellular polycarbonate case, 5.75 % from 1.5 wt% of microspheres in HDPE, and a supplier-reported 10 to 20 % less plastic with Avient's Hydrocerol grades.

Why foaming agents are nearly always dosed as masterbatch#

Blowing agents reach the machine as masterbatch in almost every thermoplastic process, because a fine reactive powder is hard to dose evenly and easy to lose as dust. Carrier resins and let-down conventions are covered on masterbatch.

Every masterbatch figure has to be converted to active content before it means anything. Eiwa's Panthlene H7351 is 70 % azodicarbonamide in a polyethylene carrier with a decomposition point of 200 °C, Polythlene EB106 is an ABS-based concentrate, and the Polythlene EE series are inorganic polyethylene masterbatches with a decomposition point of 155 °C. A 70 % active concentrate dosed at 2 % of the blend therefore delivers 1.4 % of active agent, not 2 %.

That arithmetic is where most foaming trials go wrong, because a dose quoted in a technical note is the active level while the dose set on the feeder is the concentrate level. Check any masterbatch dose with the let-down ratio calculator. Grades for injection moulding and extrusion are on foaming agent masterbatch.

How Do Blowing Agents Interact with the Rest of the Formulation?#

A blowing agent never works alone: an activator sets when the gas appears, a crosslinking peroxide or a branched resin sets whether the melt can hold it, and a nucleant sets how many cells the gas forms. Four additives work with the blowing agent and four conditions work against it.

What helps the blowing agent work is listed below.

• Activators. Zinc oxide, zinc stearate and urea pull the azodicarbonamide onset from 200-209 °C down to 140-165 °C.
• Crosslinking peroxides. BIPB at 0.5 to 0.7 phr in an EVA midsole formulation builds the network that holds the gas, reaching 78 % gel at 0.7 phr; half-lives and safe processing temperatures are on organic peroxides for polymers.
• Nucleants. Undissolved bicarbonate particles seed bubbles in gas-injection foaming, far below the level needed to expand the part.
• Melt-strength additives. Long-chain-branched grades and melt strength enhancers raise extensional viscosity, and silicone surfactants at 0.2 pphp do the same job in polyurethane.

What fights the blowing agent is listed below.

• Exothermic self-heating. Azodicarbonamide releases 1.36 kJ/g, which accelerates its own decomposition and scorches the core of a thick section.
• The barrel-temperature ceiling for microspheres. Above 220 °C expandable microspheres shrink or rupture, so the profile stays below about 180 to 190 °C.
• Chain scission in polypropylene. PP melt viscosity drops sharply above 2 kGy of electron-beam dose, so without a coagent such as TMPTMA the melt loses the strength foaming needs.
• Residue chemistry. Biurea, urazole and cyanuric acid stay in the part after ADC decomposition, with semicarbazide as a secondary product, which is the origin of foam odour and of the European food-contact restriction.

How Are Blowing Agents and Foams Tested?#

A blowing agent is characterised before it ever meets a polymer: differential scanning calorimetry gives the decomposition temperature and the heat released, thermogravimetry gives the mass loss, and a gas-volume measurement at 0 °C and 1 atm gives the yield in millilitres per gram. Those three numbers are what a grade data sheet carries, and every method on this site is indexed under testing plastic additives.

Azodicarbonamide gives 1.36 kJ/g over a 160 to 230 °C scan, and Sadik, Pillon, Carrot and Reglero Ruiz (Thermochimica Acta, 2018) established the reference calorimetry on citric acid and bicarbonate systems. Thermogravimetric analysis under ISO 11358 gives the mass loss and therefore the residue left in the part.

The finished foam is then measured rather than predicted: density from the weight and volume of a cut specimen, cell size from microscopy of a cut section, and thermal conductivity from a steady-state heat-flow measurement. No standard number is given for those three measurements on this site, because none is established in our sources.

Table T7. Test matrix for blowing agents and foams.

This site does not publish the UL 94 HF-1 and HF-2 afterflame times, because they could not be verified against the UL 94 text. Density, cell size and thermal conductivity are reported as measurements rather than as standard numbers, for the same reason.

How Are Blowing Agents Regulated?#

Blowing agents are regulated in 3 layers: climate rules that target the fluorinated physical agents, food-contact rules that decide which agents may touch food, and chemicals rules that classify and restrict the organic agents themselves. An agent clear in one layer can be blocked in another: azodicarbonamide passes every climate rule and fails the European food-contact one, while HFO-1336mzz(Z) faces a dated European ban instead. Every instrument below is summarised in plastic additive regulations.

Table T8. Regulatory instruments for blowing agents.

F-gas and AIM Act rules for fluorinated blowing agents#

The European Union has banned foams containing fluorinated greenhouse gases from 1 January 2033 unless they are required to meet safety requirements, and that ban covers the fourth-generation HFOs as well as the HFCs they replaced. Regulation (EU) 2024/573, published in the Official Journal on 20 February 2024, sets the sequence in Annex IV point 17: extruded polystyrene using HFCs with a GWP of 150 or more since 1 January 2020, all other foams using such HFCs since 1 January 2023, and every foam containing a fluorinated greenhouse gas from 1 January 2033. One-component foam with a GWP of 150 or more has been banned since 4 July 2008 under point 16, a destruction duty applies when F-gas foam panels are removed from 1 January 2025 under Article 8(8) and 8(9), and exporting foams with an F-gas GWP of 1000 or more has been banned since 12 March 2025.

Since 1 January 2025, 40 CFR 84.54 has prohibited the manufacture and import of foam made with regulated substances of GWP 150 or more across rigid, flexible and integral-skin polyurethane, XPS boardstock, phenolic and PIR boardstock, polyolefin foam and spray foam. Space and military uses follow on 1 January 2026, and sale, distribution and export are banned three years after each date. The full timetable, subsector by subsector, is on F-gas rules for foam blowing agents.

The CF3 group in HCFO-1233zd(E), HFO-1336mzz(Z) and HFO-1234ze places all three inside the OECD definition of PFAS, and the EU universal PFAS restriction is pending, with no adopted scope or date. The pending restriction and what it covers are on PFAS in plastics.

Food contact: EU 10/2011 and 21 CFR 178.3010#

Only the endothermic and physical routes are open for food-contact foam in the European Union: carbonic acid salts (FCM 21), citric acid (FCM 139), carbon dioxide (FCM 307), n-pentane (FCM 244), isopentane (FCM 143) and 1,1-difluoroethane (FCM 131) are on the Union list, while azodicarbonamide is not. Union-list mechanics are on EU 10/2011: a substance absent from Annex I may not be used at all.

Commission Directive 2004/1/EC suspended azodicarbonamide's use as a blowing agent in plastic food-contact materials from 2 August 2005, because semicarbazide was found to form from it. That suspension covers food-contact plastics only, not PVC flooring, wallpaper, footwear or technical foam.

The United States lists permitted uses with ceilings instead of a positive list. 21 CFR 178.3010 permits azodicarbonamide at up to 5 % of the finished foamed polyethylene, and permits n-pentane, isopentane and 1,1-difluoroethane in polystyrene, while 21 CFR 177.1210 covers closure-sealing gaskets at up to 2 % of the composition, or 5 % in polyethylene gaskets. The agency opened a post-market assessment of azodicarbonamide on 19 August 2025, published its Request for Information on 13 May 2026 (91 FR 27060, docket FDA-2026-N-4126) and closed the comment period on 13 July 2026 without reopening it; no outcome has been published. The 21 CFR sections are mapped on FDA food contact rules.

REACH, CLP and SVHC status of blowing agents#

Azodicarbonamide has been on the REACH Candidate List since 19 December 2012 because of its respiratory sensitising properties, and its harmonised classification is Resp. Sens. 1 with hazard statement H334. It was listed under Article 57(f), it carries CLP Annex VI index number 611-028-00-3, and it was not on Annex XIV when ECHA CHEM was checked on 22 September 2026. Every listed additive and its date is on SVHC Candidate List.

Candidate List status carries a supply-chain duty rather than a ban: above 0.1 % w/w in an article the supplier owes information under REACH Article 33 and a SCIP notification to ECHA.

The rest of the family carries classification duties without Candidate List entries. OBSH holds Self-react. D, H242 plus H400 and H410, and TSH holds Self-react. D, H242 under index 607-759-00-2. TSSC has no active REACH registration on ECHA CHEM, and 5-phenyltetrazole is registered as an intermediate only. Cyclopentane and pentane are fully registered and are not on the Candidate List as of the November 2025 update, the most recent compilation we have checked. Dicumyl peroxide, paired with azodicarbonamide in crosslinked foam, joined the Candidate List on 27 June 2024. Registration, Article 33 and SCIP duties are explained on REACH and plastic additives.

Who Makes Blowing Agents? Suppliers and Trade Names#

No single company makes the whole range: chemical blowing agents come from specialist chemical producers and masterbatchers, fluorinated physical agents come from the fluorochemical majors, and expandable microspheres come from a handful of encapsulation specialists. Eiwa Chemical is the reference case for the chemical half, because its brands map onto the type classification used on this page: Vinyfor for azodicarbonamide, Neocellborn for OBSH, Cellborn for bicarbonate systems, Spangcell for ADC/OBSH blends, and Panthlene and Polythlene for the masterbatch forms. Company profiles are in the directory of plastic additive manufacturers and suppliers.

Table T9a. Blowing agent producers and trade names.

Ownership of the Celogen and Genitron blowing-agent lines is not confirmed in our sources and is therefore not stated. Nouryon was renamed from AkzoNobel Specialty Chemicals on 9 October 2018, and Avient was formed as PolyOne on 31 August 2000.

A full buyer directory with locations and grades is on blowing agent manufacturers and suppliers.

Complete List of Blowing Agent Substances (14 Pages)#

The 14 blowing-agent substances covered on this site are listed below with their CAS number, type, decomposition or boiling point, gas released and regulatory headline. Rows follow the type order of Table T1, and no value here is new.

Table T9. The 14 blowing-agent substances covered on this site.

Each row links onward to the full record, with identity, dosage and the complete regulatory matrix, in the plastic additives database.

Are Blowing Agents Safe for Health and the Environment?#

Blowing agents raise two separate safety questions: azodicarbonamide is a respiratory sensitiser and sits on the REACH Candidate List, while the fluorinated physical agents are regulated for their effect on the climate rather than on health. Cyclopentane and pentane are flammable, but neither is a fluorinated greenhouse gas or a substance of very high concern, and nitrogen and carbon dioxide raise neither question. Where blowing agents sit among the substances of concern is on toxic plastic additives.

Why is azodicarbonamide on the REACH Candidate List?#

Azodicarbonamide was added to the REACH Candidate List on 19 December 2012 because it can cause asthma and allergic reactions if the dust is inhaled, which is an occupational exposure question in compounding plants rather than a consumer one. The listing was made under Article 57(f), and the harmonised classification Resp. Sens. 1, H334 carries the same finding into every safety data sheet.

Two consequences follow for anyone handling it: dust control and respiratory protection govern weighing and compounding, which is one reason the masterbatch form dominates, and above 0.1 % w/w in an article the Article 33 duty and a SCIP notification apply. It is not on Annex XIV, so no authorisation is required.

From CFCs to HFOs: how climate rules rewrote the blowing-agent market#

Foam blowing has changed chemistry four times in forty years: chlorofluorocarbons gave way to HCFCs under the Montreal Protocol, HCFCs to HFCs, and HFCs to the fourth-generation HFOs and HCFOs whose global warming potentials are 3.88 and 2.08 instead of 1030. Each substitution worked because the boiling points are close enough to be drop-in, from HCFC-141b at 32.0 °C and HFC-245fa at 15.3 °C to HCFO-1233zd(E) at 19.3 °C and HFO-1336mzz(Z) at 33.4 °C.

What comes next is not settled. The 1 January 2033 European ban reaches the fourth generation too, and the PFAS question is pending. Ian Cousins and colleagues at Stockholm University published a multi-criteria assessment of non-fluorinated alternatives for insulation foam in RSC Sustainability in 2026, the direction the hydrocarbon, oxygenate and inert-gas routes already point.

Do blowing agents make plastics harder to recycle?#

Chemical blowing agents are one of the few additive families that recyclers rate positively: the Association of Plastic Recyclers lists them among the workhorse additives rated Design Preferred for rigid polypropylene. That rating puts them alongside thermal stabilizers, UV stabilizers, nucleating agents, antistatic agents, lubricants, fillers, pigments and impact modifiers, and contrasts with degradable additives, which make the same package non-recyclable.

The harder problem is structural: crosslinked foam is a network that cannot be remelted, and the dicumyl peroxide used to make it joined the Candidate List on 27 June 2024. The APR and EuCertPlast criteria are on design for recycling.

What is the blowing agent in a refrigerator?#

The blowing agent in a refrigerator is the gas trapped in the rigid polyurethane foam inside the cabinet walls, not the refrigerant that circulates in the cooling loop. Cyclopentane, boiling at 49.2 °C, is the usual European appliance choice: zero ozone depletion potential, a very low global warming potential and no exposure to the F-gas foam bans, at the cost of a flammable process. HCFO-1233zd(E) is the low-GWP fluorinated alternative at a GWP100 of 3.88, and in the United States appliance rigid polyurethane falls under the 40 CFR 84.54 GWP-150 limit since 1 January 2025.

Is a concrete, fire-fighting, rubber or soap foaming agent the same thing?#

No: a concrete or soap foaming agent is a surfactant that traps air in a liquid, while a plastics blowing agent generates gas inside a polymer melt. Fire-fighting foam concentrates are a third class again, governed by their own REACH restriction, and rubber blowing agents overlap chemically, since DPT (CAS 101-25-7, decomposing at 205 °C with a gas volume of 242 mL/g) and azodicarbonamide itself are both used in sponge rubber, but pure rubber chemistry falls outside the scope of this site.