Metal Stearates: 7 Types, 5 Functions in Plastics, Dosage and Selection

Metal stearates, also called metallic stearates or metal soaps, are the metal salts of stearic acid (octadecanoic acid, CAS 57-11-4), and the seven used in plastics are the calcium, zinc, magnesium, aluminium, lithium, sodium and lead salts, plus the transition-metal stearates used as pro-oxidants. One compound can use the same powder as a lubricant, an acid scavenger, a mould release agent, a co-stabilizer and a dispersion aid, which is why the choice between calcium and zinc stearate is rarely obvious.

Metal soaps are among the oldest and highest-tonnage groups of plastic additives, and a rigid PVC pipe formulation still carries 0.4 to 1.5 phr of calcium stearate. A polyolefin compound needs far less, 0.05 to 0.20 % of a metal soap, because in that polymer the powder scavenges catalyst residue rather than lubricating the melt. The metal decides which of the two jobs a given grade is bought for, and that single decision runs through every section below.

This page covers the four production routes, the five functions, the seven metal stearates from calcium to the transition-metal pro-oxidants, calcium versus zinc, phr and ppm dosage, how the effect is tested, EU and US food-contact and REACH status, and the producers that supply them.

Key figures

• Calcium stearate: CAS 1592-23-0, melts at about 160 °C and is classed as an internal lubricant (Baerlocher)
• Zinc stearate: CAS 557-05-1, melts at about 120 °C and is classed as an external lubricant (Baerlocher)
• Polyolefin acid-scavenger level: 0.05 to 0.20 % of a metal soap
• No metal stearate carries its own EU food-contact number; all are covered as salts of stearic acid, FCM No 106, under Article 6(3)(a) of Regulation (EU) No 10/2011

What Are Metal Stearates?#

Metal stearates are metal soaps: salts in which a divalent or trivalent metal ion replaces the acidic hydrogen of stearic acid, giving a powder with a polar carboxylate head and two or three non-polar C18 tails. The polarity and the chain length of that tail decide how the powder behaves in a melt. Polar moieties such as -OH, -COO- and -COO-Ca sitting on a C14-18 chain act as internal lubricants, while non-polar chains above about C20, running up to roughly C100, act as external lubricants. Peter Greven's own summary of the rule is blunt: "a reduction in polarity leads to products with external lubricating effects."

The hub on processing lubricants for plastics places metal soaps next to the waxes, esters and amides that share the same friction-lowering job. Within that group, the carboxylate head sets metal stearates apart: it is the reactive site that lets the same molecule also scavenge acid, release a mould, or wet a pigment surface, jobs a plain hydrocarbon wax cannot do.

How are metal stearates made?#

Metal stearates are made by reacting stearic acid or its sodium soap with a metal salt or metal base, and the four industrial routes are indirect precipitation, direct conversion, the melt process and a continuous process. Every route starts from stearic acid in plastics or from its sodium soap, and the route chosen fixes the particle shape, the purity and, ultimately, the price of the grade.

1. Indirect precipitation reacts a sodium stearate solution with a soluble metal salt, giving a very fine, high-surface-area, low-bulk-density powder with a higher salt content than the other routes produce.
2. Direct conversion adds a metal base powder to stearic acid below the soap's own melting point, giving a product with a pH above 7.
3. The melt process reacts the components above the melting point of the resulting soap, giving a dust-free, clear melt that solidifies into flakes or pastilles.
4. A continuous process runs the same chemistry as a continuous reaction rather than a batch, giving a dust-free, neutral-pH, layered particle that dissolves faster and carries a low filter index.

The route matters because it is read straight off the grade's physical form. Baerlocher's SMS flakes and TX pastilles are melt products: dust-free, silo-storable and resistant to abrasion. Its AV granules come from a different finishing step and give very low dust with a high bulk density.

What is the filter index of a metal stearate?#

The filter index, measured in bar per kilogram, says how quickly a stearate blocks a melt filter, and it is the specification that decides whether a grade can be used in polypropylene fibre and film. A high filter index means the melt filter clogs faster and the line has to stop sooner to change it, so fibre and film producers screen grades on this number before they screen on price. No numeric pass or fail value for the filter index is established in the sources behind this page, so this page states the specification without a target figure.

What do metal content, free fatty acid and ash tell you about a grade?#

A metal stearate data sheet is read through four numbers: metal content, melting range, free fatty acid and ash, because they fix how much soap is really in the powder and how it behaves in the melt. Metal content confirms the salt has formed completely; free fatty acid and ash show how much unreacted stearic acid and inorganic residue the grade still carries; and the melting range, always reported for both the pure substance and the commercial grade, sets the temperature window in which the lubricant starts to work.

The 6.3-7.9 % calcium range spans several supplier grades rather than a single specification, so this page keeps the wider, qualified figure. The gap between a pure substance's melting point and a commercial grade's melting range, up to 39 °C for calcium stearate, is not an error: technical grades are blends and never reach the purity of the reference compound PubChem reports.

What Do Metal Stearates Do in Plastics? The 5 Functions#

The 5 functions of metal stearates in plastics are lubrication of the melt, acid scavenging in polyolefins, internal mould release, co-stabilization of PVC in calcium-zinc systems, and wetting and dispersion of pigments and fillers. They are ordered here by tonnage and by how often each function is the actual reason a compounder buys the powder in the first place.

1. Lubricant in PVC and other melts#

As a lubricant, a metal stearate lowers friction in two places at once: between the polymer particles and chains inside the melt, and between the melt and the hot steel of the screw, die or calender roll. Baerlocher classifies calcium stearate as internal, melting at about 160 °C, and zinc stearate as external, melting at about 120 °C; zinc stearate's low melting point "means it spreads very evenly when heated," in the company's own phrasing. Internal lubricants lower inner friction, torque and melt viscosity without affecting fusion time or haze, while external lubricants release more metal at the wall, prolong fusion, and can cause haze, exudation and reduced printability at high dosage.

Between the polymer particles, the lubricant controls how fast the PVC grains fuse into a continuous melt; at the metal wall, it controls how much torque the extruder or calender needs and how easily the melt releases from hot steel. How the whole package is balanced across both locations is set out under lubricants for PVC compounding.

Internal or external: why the labels mislead#

Elvira Rabinovitch, Lacatus and James Summers showed in 1984 that the internal and external labels are deficient in explaining performance: it is the polar calcium stearate, not the non-polar paraffin, that wets hot metal, and the paraffin works by making the calcium stearate layer more fluid. Their combined DTA, haze, microscopy, metal-release and Brabender fusion data found that lubrication between PVC primary particles follows the same physics as lubrication at the metal wall. Krzewki and Collins reported a related complication in 1981: calcium stearate can accelerate or delay PVC fusion depending on temperature and on whether wax is present, enhancing fusion once wax is in the package and delaying particle breakdown when it is not.

2. Acid scavenger and catalyst neutralizer in polyolefins#

In polyolefins the stearate is bought as an acid scavenger, not as a lubricant: at 0.05 to 0.20 % it neutralizes the chloride left by the Ziegler-Natta catalyst before it can corrode the screw or attack the stabilizer package. Calcium stearate is used up to 1,000 ppm for this job, and Peter Greven reports that a 500 ppm level prevented a steel plate corroding in a polypropylene test. The full mechanism and the three-way comparison against hydrotalcite and zinc oxide sit on acid scavengers and catalyst neutralizers.

Espelage et al. (2025) found that more Irgafos 168 was retained after compounding when calcium stearate was present, evidence the soap also protects the antioxidant package, while a 2023 review notes it may act as a pro-oxidant under natural weathering, a finding kept conditional here. In PP raffia and BOPP film the calcium chloride formed is hygroscopic, raising water carry-over, and Kisuma reports as a supplier observation that stearate migration can impair metallization on those films.

3. Internal mold release agent#

As an internal mold release agent the stearate is compounded into the plastic rather than sprayed on the tool, and it migrates to the part surface during moulding to form a thin parting layer. The full class of internal mold release agents covers esters and amides as well as soaps, but the metal stearates are the oldest members of the group.

• SMC and BMC, where zinc stearate is preferred because of its lower melting point, and precipitated grades release best because of their fineness; a coarser stearate raises paste viscosity less at the same dosage, and Peter Greven used 1.23 wt% in its own Brookfield viscosity test.
• PLA injection moulding, where Tábi and Pölöskei (2021) found that calcium stearate at 1 wt% eliminated stuck and broken parts, a result PLA processing literature cites often.
• General plastics, where zinc stearate is used at about 0.5 % across most polymer types (Struktol), and magnesium stearate at 0.3 to 3 parts in ABS, doubling as a dusting agent against surface adhesion.

4. Co-stabilizer in calcium-zinc PVC systems#

In PVC the same two soaps do a second job: the zinc soap replaces the labile chlorine atoms that start dehydrochlorination, and the calcium soap regenerates the zinc soap from the zinc chloride that forms. The reaction, ZnCl2 + Ca(O2CR)2 to CaCl2 + Zn(O2CR)2, keeps the zinc site active far longer than a single-metal soap could alone. The full system, including the five co-stabilizer classes used with it, is described on calcium-zinc stabilizers.

The zinc chloride produced is a Lewis acid, and its build-up causes zinc burning, a sudden loss of colour stability that the calcium regeneration reaction only partly controls. Polyols, phosphites, beta-diketones and hydrotalcite are the co-stabilizers most often added to hold it back, and a preblended calcium-zinc soap melts at about 100 °C, some 20 to 30 °C below either single soap.

5. Dispersion, wetting and flow aid in masterbatch and filled compounds#

The fifth job is dispersion: the polar head of the soap wets the surface of a pigment or a mineral filler, and the C18 tails make that surface compatible with the polymer melt. Calcium stearate is the grade most often used to wet pigments in colour concentrates, and the same wetting action controls processability in heavily filled compounds.

Radebe et al. (2022, University of Pretoria, Focke) measured the melt viscosity of a 60 wt% calcium carbonate masterbatch in LLDPE at three times that of the neat polymer, and found that 3 wt% wax plus 1.0 wt% zinc stearate brought viscosity back to just above the neat resin; magnesium stearate alone was less effective, but a blend of the two performed well. Most stearate reaches the converter already inside a masterbatch carrier, the same route by which coated grades of calcium carbonate in plastics arrive: stearic acid coats the filler at about 1.1 % of its weight in one documented grade, and stearate-coated chalk is used at 5 to 15 % in uPVC window profiles.

Which 7 Metal Stearates Are Used in Plastics?#

The 7 metal stearates used in plastics are calcium, zinc, magnesium, aluminium, lithium and sodium stearate plus lead stearate, and a small group of transition-metal stearates is used for the opposite purpose, to make polyethylene degrade. They are ordered here by tonnage in plastics, ending with the two restricted groups, lead and the pro-oxidants.

1. Calcium stearate#

Calcium stearate (CAS 1592-23-0, EC 216-472-8, 607.0 g/mol) is the highest-volume metal stearate in plastics and the only one that appears in all five roles. Pure-substance data give a melting point of 179 °C (PubChem), while commercial grades run 140-165 °C (Struktol) or about 160 °C (Baerlocher CA 600), a gap of up to 39 °C that reflects blend purity, not an inconsistency in the sources.

Beyond PVC, calcium stearate is also used in polyamide and SAN, and it carries the food additive designation E 470a (salts of fatty acids). The full property and regulatory record for calcium stearate sits on its own substance page.

2. Zinc stearate#

Zinc stearate (CAS 557-05-1, EC 209-151-9, 632.3 g/mol) melts between about 115 and 130 °C, roughly 40 °C below calcium stearate, and that single property explains most of its behaviour. PubChem and NIOSH report 130 °C for the pure substance and Struktol quotes 115-125 °C for commercial grades, with a density of 1.095 g/cm3 at 25 °C and a zinc content of 10.4 to 11.3 %.

Grades and the full hazard record are on zinc stearate. Zinc stearate also forms colourless zinc-quinone complexes, which suppresses the pinking that over-oxidised phenolic antioxidants otherwise cause in white polyolefins, and it is a formulated component, at one third by mass, of the nucleating agent Hyperform HPN-20E.

3. Magnesium stearate#

Magnesium stearate (CAS 557-04-0, EC 209-150-3, 591.2 g/mol) is the specialist of the three: in plastics it is used mainly as a lubricant and release agent for ABS, SAN and polyamide, and as a dusting agent that stops ABS parts sticking to each other. PubChem gives 88.5 °C for the pure substance and 132 °C for the technical grade, while Struktol's range for commercial grades is 125-145 °C; magnesium content runs 4.0 to 4.8 %.

The plastics record separates the ABS lubricant, dosed at 0.3 to 3 parts (Struktol), from the tablet grade sold to the pharmaceutical industry, chemically the same salt but specified to a different purity standard. The "magnesium stearate benefits" search cluster belongs to that pharmaceutical grade and is answered only in a short supplementary note below the contextual border, not here.

4. Aluminium stearates#

Aluminium stearates exist as mono-, di- and tri-stearates, and aluminium tristearate (CAS 637-12-7) carries a single active REACH registration, which shows how much smaller its plastics volume is than calcium's or zinc's. In the United States the same substance is spelled aluminum stearate, and it is not classified in 99.6 % of its C&L notifications. The EU Annex II specific migration limit for aluminium is 1 mg/kg. No plastics dosage or function claim for aluminium stearate is established in our sources, so none is given here.

5. Lithium and sodium stearates#

Lithium stearate (CAS 4485-12-5) and sodium stearate are the minor members of the group in plastics, and the European food-contact rules treat them very differently: lithium carries a specific migration limit of 0.6 mg/kg, while sodium has none. Lithium stearate holds 4 active REACH registrations and is not classified in 100 % of its C&L notifications. No CAS number, dosage or function record for sodium stearate exists in our sources; it is named here because supplier catalogues list it, but nothing further can be stated about it truthfully.

6. Lead stearate and dibasic lead stearate#

Lead stearate and dibasic lead stearate were the workhorse lubricant-stabilizers of European PVC until the lead phase-out, and they are the only members of this group that carry a REACH Candidate List entry. Lead distearate is CAS 1072-35-1, EC 214-005-2, C36H70O4Pb, 774.1 g/mol, melting at about 115.7 °C with a density of 1.34-1.4; dibasic lead stearate (DBLS, dioxobis(stearato)trilead) is CAS 12578-12-0, EC 235-702-8, about 1,220.6 g/mol.

DBLS and the group entry "Fatty acids, C16-18, lead salts" (CAS 91031-62-8) have been on the REACH Candidate List since 19 December 2012 as toxic for reproduction under Article 57(c), but neutral lead distearate is not individually listed. ECHA's ninth Annex XIV recommendation of 21 October 2019 covered dibasic lead stearate, and none of the seven lead compounds reviewed was added to Annex XIV, so lead stearate does not require authorisation. Lead in PVC is instead restricted under REACH Annex XVII entry 63 (Regulation (EU) 2023/923): below 0.1 % from 29 November 2024, with recovered rigid PVC allowed up to 1.5 % until 28 May 2033. The Candidate List entries and the phase-out timeline are recorded on the lead stearate and dibasic lead stearate substance record.

7. Pro-oxidant stearates: cobalt, iron and manganese#

Cobalt, iron and manganese stearates are used for the opposite purpose to the other six: they catalyse the oxidation of polyethylene rather than protect it, and their pro-oxidant strength rises in the order iron, manganese, cobalt. Cobalt stearate is CAS 13586-84-0 (EC 237-016-4, also indexed as 1002-88-6), C36H70CoO4, 625.9 g/mol, and iron(III) tristearate is CAS 555-36-2. Cobalt stearate is not on the Candidate List and is permitted in EU food contact through the Article 6(3)(a) salt rule, with a cobalt-specific migration limit of 0.05 mg/kg.

Cobalt stearate is the strongest of the three and the only one with an EFSA opinion: the EFSA CEP Panel concluded in 2022, on a PCOE-plus-cobalt-stearate oxygen scavenger, that it was "not able to conclude on safety," a finding this page states without softening or extending it. Products made of oxo-degradable plastic have been prohibited in the EU since 3 July 2021 under Article 5 of Directive (EU) 2019/904, the wording the directive itself uses. The evidence and the EU ban are set out in a dedicated guide to oxo-degradable plastics.

Calcium Stearate vs Zinc Stearate: Which One Do You Need?#

Calcium stearate is the default whenever thermal stability, acid scavenging or food-contact headroom decide the choice, while zinc stearate wins where a low melting point and clean mould release matter more. No published source in our source library resolves which soap is generally "better," so this page compares them only on the documented properties below rather than declaring an overall winner.

The single most useful decision rule is regulatory rather than mechanical: zinc is the only one of the three that carries a metal migration limit in EU food contact, 5 mg/kg since Regulation (EU) 2020/1245 (previously 25 mg/kg), and it is the only one of the three with a substantial minority of aquatic-hazard notifications. A formulator working close to a food-contact metal budget, or avoiding an aquatic hazard classification on the safety data sheet, has a clear reason to prefer calcium or magnesium stearate even where zinc's lower melting point would otherwise be convenient.

Can calcium stearate and zinc stearate be used together?#

Yes: the calcium-zinc pair is the standard lead-free PVC stabilizer system, and a preblended calcium-zinc soap melts at about 100 °C, some 20 to 30 °C below either single soap. The two soaps have complementary roles rather than overlapping ones, zinc replacing labile chlorine and calcium regenerating the zinc site, which is why they are formulated together rather than substituted for each other in a one-pack stabilizer.

How Much Metal Stearate Does a Compound Need?#

Metal stearate levels run from 500 ppm in a polypropylene grade to 8 parts in a wood-filled PVC compound, and the unit changes with the polymer: phr for PVC and wood composites, ppm or wt% for polyolefins. PVC formulators always quote PHR (parts per hundred resin), never weight percent, because every other ingredient in a PVC compound is also indexed to 100 parts of resin.

Converting between the two units by hand is the most common formulation error at this step, since a phr figure and a weight-percent figure are numerically different once fillers or pigments are in the recipe. The PHR to weight percent calculator converts a full package in one step, including the PPI worked example given below.

Rigid PVC lubricant packages in phr#

A rigid PVC pipe compound carries 0.6 to 1.5 phr of calcium stearate, paired with the same amount of paraffin wax and 0.1 to 0.2 phr of an oxidized polyethylene wax.

Supplier technical data sheets and the PPI TR-2 range composition. Trials decide the final level.

Clear injection moulding is the one package in the table that carries no stearate at all: paraffin wax is "not recommended for articles that are to be printed" in Struktol's own note, and clear compounds use esters instead of a stearate to avoid the haze a metal soap can add. Oxidized polyethylene wax supplies the metal release that the stearate alone cannot, which is why it appears alongside calcium stearate in every opaque package rather than replacing it.

The Plastics Pipe Institute's TR-2 Appendix C gives a fully worked pressure-pipe formulation: PVC 100, heat stabilizer 0.70, paraffin 1.20, PE wax 0.15, CaCO3 5.00, TiO2 0.50, pigment 0.03 and calcium stearate 0.45 phr, for a total of 108.03 phr, of which PVC is 92.57 wt% of the compound. The PPI's own range for calcium stearate across pressure-pipe formulations is 0.4 to 1.5 phr, and Struktol advises formulators to "reduce calcium stearate as much as possible for improved flow," a modality worth keeping in mind before adding a safety margin on top of a supplier's starting point. The complete pipe and profile recipes sit in the rigid PVC formulations guide.

Polyolefin acid-scavenger levels in ppm#

Polyolefin grades use far less: 0.05 to 0.20 % of a metal soap is enough to neutralize catalyst residues, and 500 ppm of calcium stearate was enough to stop a steel plate corroding in a polypropylene test. The three-way comparison against hydrotalcite and zinc oxide, including the full selection decision, sits in the dedicated guide to acid scavengers for polyolefins.

Three factors drive the level chosen within that range in practice.

• Catalyst residue load, since a higher residual chloride from the polymerization step needs a proportionally higher scavenger dose to neutralize.
• Surface requirements, because a film that will be metallized or printed is more sensitive to the hygroscopic calcium chloride byproduct than an unprinted moulding is.
• The rest of the stabilizer package, since more stearate present at compounding was shown to retain more Irgafos 168 after processing (Espelage et al. 2025), which can justify dosing toward the top of the range even where corrosion protection alone would not.

Over-lubrication: plate-out, haze and exudation#

Too much stearate is as damaging as too little: over-lubrication shows up as plate-out on calender rolls and dies, haze in clear compounds, surface exudation, and poor printing and welding. External lubricants at high dosage are the more frequent cause, because their whole function is to migrate to the surface, and Struktol's flow guidance to reduce calcium stearate as much as possible reflects the same trade-off from the internal-lubricant side.

• Plate-out on calender rolls and dies, which forces a cleaning stop and can mark the next few metres of product
• Haze in compounds meant to stay clear, from lubricant that has not stayed dissolved in the melt
• Surface exudation, a visible film that can attract dust or resist printing ink
• Reduced printability, weldability and adhesion, all consequences of a lubricant-rich surface layer that a coating or a weld bead cannot key into

Musil and Zatloukal name metallic stearates in Ziegler-Natta polyolefins among the contributors to die drool, alongside the low-molecular-weight fraction of multimodal polyethylene, hexane extractables and volatile stabilizers, which places stearate over-lubrication in the same failure family as several other additive-related processing defects. Causes and cures for the PVC-specific version of this problem are collected under plate-out in PVC processing.

How Is the Effect of a Metal Stearate Tested?#

The effect of a metal stearate is measured on the compound, not on the powder: fusion time and torque in a torque rheometer, melt flow rate to ISO 1133, wall shear stress in a capillary rheometer, and filter index for fibre and film grades. None of the grade specifications in the table above (metal content, melting range, free fatty acid, ash) predicts processing behaviour on its own, which is why every supplier package is trialled on the actual compound before it is locked in.

1. Torque rheometer (Brabender) fusion testing, which plots torque against time and reads fusion time and equilibrium torque directly from the curve.
2. Melt flow rate, measured to ISO 1133 or ASTM D1238, the fastest single check that a lubricant change has actually moved the melt.
3. Capillary rheometry, to ASTM D3835, the method also cited in 21 CFR 177.1520 for fluoropolymer processing aids and a useful cross-check for wall shear stress.
4. Filter index testing, for polypropylene fibre and film grades, where a rising filter index signals a grade change or contamination before it shows up as a hole in the film.

Formulators should confirm a lubricant change with at least two of these methods together, rather than reading a single number in isolation. Torque curves and fusion time are explained in the PVC fusion testing guide, and melt flow rate is the quickest check that a change moved the melt at all.

Are Metal Stearates Allowed in Food-Contact Plastics?#

Metal stearates have no food-contact authorisation of their own: in the EU they are allowed as salts of an authorised acid, and in the US the calcium, zinc and magnesium salts are separately listed as generally recognised as safe. Neither region ever describes them as "FDA approved" or "EU approved"; the correct language is always the specific listing, and this page uses it throughout.

EU 10/2011: the salt rule and the Annex II metal limits#

In the European Union a metal stearate is never listed as such: Regulation (EU) No 10/2011 authorises stearic acid as FCM No 106, and Article 6(3)(a) extends that authorisation to its salts, subject to the metal limits in Annex II. No metal stearate is given an FCM number of its own; the salt rule is the only route by which any of them reaches a food-contact plastic.

The overall migration limit that applies regardless of metal is 10 mg/dm2, and where no specific migration limit is listed, the generic limit of 60 mg/kg applies under Article 11(2). A related salt, 12-hydroxystearic acid, is separately listed as FCM No 214 with no specific migration limit of its own. How the salt rule and the migration limits interact is explained on EU 10/2011.

US FDA: GRAS listings and prior-sanctioned use#

In the United States the three main metal stearates are covered as food substances rather than as plastics additives: calcium stearate under 21 CFR 184.1229, zinc stearate under 21 CFR 182.8994 and magnesium stearate under 21 CFR 184.1440.

• Calcium stearate, GRAS under 21 CFR 184.1229, and also listed as a prior-sanctioned stabilizer in food packaging under 21 CFR 181.29
• Zinc stearate, GRAS under 21 CFR 182.8994
• Magnesium stearate, GRAS under 21 CFR 184.1440, and also listed under 21 CFR 181.29
• Stearic acid itself, GRAS under 21 CFR 184.1090, the parent acid all three salts share

Section 181.29 also sets a 50 ppm migrant limit for stannous stearate, expressed as tin, and for zinc orthophosphate and zinc resinate, expressed as zinc, but lists calcium stearate with no limit stated. The 184.1229 text itself prints CAS 1529-23-0, a typo for calcium stearate's correct number, 1592-23-0, worth flagging for anyone checking the regulation against the CAS number. GRAS status, prior sanction and a food-contact notification are distinguished on FDA food contact rules for plastic additives.

REACH registration, SVHC status and hazard classification#

Calcium, zinc and magnesium stearate are all registered or self-classified industrial substances, and none of the three is on the REACH Candidate List as of 22 September 2026.

These figures come from aggregated C&L notifications, not a harmonised classification, so this page never states that "zinc stearate is classified as H400." No active REACH dossier was found for magnesium distearate under CAS 557-04-0 on 22 September 2026, stated here as an absence of a found record, not as proof of non-registration under a different identifier. Registration, the Candidate List and Annex XVII are explained on REACH and plastic additives.

Who Makes Metal Stearates?#

Metal stearates are made by a small group of specialists: Baerlocher, Peter Greven, Struktol, Valtris and PMC Biogenix, and each sells the same three main salts under its own brand. Buyers should compare grades by metal content, melting range and filter index, not by brand name, because the underlying chemistry is the same salt regardless of which company supplies it.

Only the brand names listed above are established in the sources behind this page; several other names appear in search results for metal stearates without a confirmed company behind them in our records, so this page does not repeat them. Plants, grades and certifications by company are collected in the directory of calcium and zinc stearate manufacturers, and price drivers and grade differences are tracked on the calcium and zinc stearate prices page. No verified market size, growth rate or price figure for metal stearates is established in our sources, so none is published on this page.

What Other Lubricants Work Alongside Metal Stearates?#

A metal stearate almost never works alone: in every published PVC package it sits next to a hydrocarbon wax, and often next to an ester or a bis-amide that does the part of the job the soap cannot. The complete PVC package, including how every lubricant class in it is balanced, is on additives for PVC.

Waxes and ester lubricants compared with metal stearates#

Ranked by melting point, the PVC lubricant shelf runs from paraffin at 54 to 56 °C through polyethylene wax at 102 to 110 °C and zinc stearate at about 120 °C to calcium stearate at about 160 °C. Glycerol monostearate, at 40 % monoester content, melts at 56-62 °C and is classed internal; fatty acids melt at 54-60 °C and hydroxy fatty acids at 70-80 °C, both external; and ethylene bis-stearamide melts higher still, at 138-144 °C, also external.

The full melting-point and molecular-mass table for the whole shelf is on polymer waxes, and ethylene bis stearamide (EBS) melts about 20 °C below calcium stearate while dispersing pigment about as well as it lubricates. Clear PVC formulations use ester lubricants instead of a stearate, since a soap that melts near 160 °C is harder to keep fully dissolved in a thin, optically clear section.

Metal stearates in polypropylene, polyethylene and wood-plastic composites#

Outside PVC the three biggest uses are acid scavenging in polypropylene, viscosity control in filled polyethylene masterbatch, and the heavy lubricant packages that wood-plastic composites need. Where the acid scavenger sits inside the whole PP additive package, alongside the antioxidant, HALS and nucleating agent, is shown on additives for polypropylene.

Wood-filled PVC uses 2 to 8 parts of a blended lubricant, and wood-filled polyolefin uses 1 to 6 % of the compound, with amide-and-metal-soap blends run at 1.0 to 3.0 %, all higher than an unfilled compound needs because the wood flour absorbs part of the dose before it reaches the polymer-metal interface.

Is calcium stearate the same as stearic acid?#

No: stearic acid (CAS 57-11-4, 284.5 g/mol) is the free fatty acid and the raw material, while calcium stearate (CAS 1592-23-0, 607.0 g/mol) is its calcium salt, and the salt melts about 100 °C higher. Stearic acid itself melts at 69.3 °C as the pure acid, or 54-64 °C in commercial fatty-acid lubricant blends, and it is also used directly as an external PVC lubricant and as a calcium carbonate filler coating.

Are metal stearates plant-based?#

Sometimes: stearic acid is the C18 saturated fatty acid found in both vegetable and animal fats, so whether a specific metal stearate grade is plant-based depends on the feedstock its supplier used, not on the chemistry of the salt. Commercial lubricant-grade stearic acid is usually a blend of C16-18 fatty acids, and the feedstock, vegetable or animal, is stated on the individual grade specification rather than being fixed by the chemical name. No vegetable-grade or RSPO certification data for any specific metal stearate grade is established in the sources behind this page.

Is magnesium stearate in supplements the same material?#

Magnesium stearate (CAS 557-04-0) sold as a tablet lubricant is the same chemical as the plastics grade, but the two are made to different purity specifications, and the nutritional questions about it are outside the scope of this plastics reference. In C&L notification data the substance is not classified in 54.9 % of 510 aggregated notifications; this page makes no health claim about the supplement use in either direction, and readers researching that use should consult a source that covers pharmaceutical excipients.

Do metal stearates cause die build-up?#

They can: Jan Musil and Martin Zatloukal name metallic stearates in Ziegler-Natta polyolefins among the contributors to die drool, next to the low-molecular-weight fraction of multimodal polyethylene and volatile stabilizers. Processing aid to inorganic pigment interactions and hexane extractables round out their list of contributors, which means a die-drool problem is rarely traced to the stearate alone without also checking the resin's own low-molecular-weight tail.

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