Ask three suppliers for a silicone elastomer gel and you will get three drums that look identical, behave completely differently, and sit in three different regulatory positions. The reason is arithmetic: a commercial elastomer gel is only 13-25% crosslinked polymer, and the remaining 75-87% is the carrier fluid. The carrier is what you buy in bulk, what evaporates or stays on skin, and - since 2024 - what decides whether the drum can legally enter the European Union.
One elastomer, three carriers, three products
| Gel (INCI) | CAS | Carrier behaviour | Non-volatile content | Viscosity at 25 degrees C | Best fit |
|---|---|---|---|---|---|
| Isododecane (and) Dimethicone Crosspolymer | 31807-55-3; 213629-14-2 | Volatile hydrocarbon; flashes off fast, leaves a dry matte film | 14-18% | 100,000-400,000 cP | Transfer-resistant lip, matte foundation, dry-touch sun care |
| Dimethicone (and) Dimethicone Crosspolymer | 9006-65-9; 63148-62-9 | Non-volatile; stays in the film, long playtime, hot-processable | 20-25% | 300,000-1,500,000 cP | Oil-phase thickener, cushion in creams, hot-fill sticks |
| Cyclopentasiloxane (and) Dimethicone Crosspolymer | 541-02-6; 63394-02-5 | Volatile D5 carrier; silky, fast dry-down, strong matte | 13-16% | 350,000-700,000 cP | Legacy matte gels - now a compliance problem in the EU |
| Acrylates/Polytrimethylsiloxymethacrylate Copolymer (and) Isododecane | 31807-55-3 | Non-elastomer film former in the same volatile carrier; holds pigment, water-resistant | supplier specific | pourable dispersion | Long-wear colour, water resistance, transfer resistance |
The two volatile gel types are not interchangeable either. An isododecane gel sets in seconds and leaves a dry, almost powdery film - the reason it dominates long-wear lip products. A cyclopentasiloxane gel spreads with more slip and dries slightly slower, which is why it built the original matte-primer category. A dimethicone-carried gel never fully dries: it keeps a cushion on skin for hours, thickens the oil phase, and tolerates the 70-80 degrees C of a hot-fill process that the volatile gels cannot survive.
The compliance question that now leads the brief
Commission Regulation (EU) 2024/1328 rewrote entry 70 of Annex XVII to REACH. From 6 June 2026, D4 (CAS 556-67-2), D5 (CAS 541-02-6) and D6 (CAS 540-97-6) may not be placed on the EU market as substances, as constituents of other substances, or in mixtures at 0.1% by weight or more. For cosmetic products a later transitional date applies - 6 June 2027 - while rinse-off cosmetics have been covered for D4 and D5 since 31 January 2020.
Put a D5 number on that: a cyclopentasiloxane-carried elastomer gel is typically 84-87% D5 by weight. A leave-on product built with 15% of that gel already carries roughly 13% D5 - more than a hundred times the 0.1% threshold. There is no blending trick that rescues it; the only routes are reformulation or relocation of the product outside the EU. That is why the isododecane and dimethicone gels have moved from "alternatives" to the default purchase in European briefs. If you sell globally, treat a D5-carried gel as a two-year transition item, not a platform.
Reading a gel certificate of analysis
- Non-volatile content is the number that converts gel dose into elastomer dose. A 18% non-volatile gel dosed at 15% delivers 2.7% elastomer. Buy on non-volatile content, not on viscosity alone.
- Viscosity is only meaningful with the spindle and speed quoted. The same 20% elastomer gel can be sold at 300,000 cP or 1,000,000 cP depending on the grade - and the choice is a sensory decision, not a quality ranking. A high-viscosity grade at the same use level gives a firmer, more cushioned film.
- Carrier identity, with its own CAS, must be printed separately from the elastomer CAS. A COA that lists only "Isododecane (and) Dimethicone Crosspolymer" without both numbers cannot be used for a regulatory dossier.
- Residual cyclics: for EU-bound product, ask for the D4, D5 and D6 content of the finished gel in ppm. A polymer-bound residual below 1% has a partial exemption when the polymer is supplied as a constituent of another substance, but the mixture you place on the market is still assessed on its own 0.1% threshold. Get the number, then run the calculation.
Use levels that actually appear in working formulas
- 3-15% as a sensory modifier and oil-control agent in anhydrous oils, serums and primers.
- 10-30% in long-wear matte foundations and concealers, where the elastomer also stabilises pigment.
- 20-60% in anhydrous matte lip glazes and glosses, where the gel is the structure rather than an additive.
Above those windows the film turns visible and starts to pill, especially over a water-based serum that has not fully dried. Pilling is a film-formation problem, not a compatibility problem - the water film disrupts the elastomer before it sets.
Processing notes worth writing into the batch record
- Cold process is possible whenever the formula contains no solid or waxy phase: mix the gel into the oil phase at room temperature.
- In water-in-oil emulsions, add 0.5-2.0% sodium chloride or another electrolyte to the water phase. Electrolytes raise the interfacial film stability and are the cheapest shelf-life insurance in a W/O system.
- Adding the water phase slowly into the oil phase under high agitation, then increasing speed, gives a more stable W/O structure than the reverse order.
- Raising the water-phase ratio generally raises final viscosity in a W/O emulsion built on an elastomer gel - the opposite of what most formulators expect.
What belongs on the purchase order
- Elastomer INCI plus carrier INCI, each with its own CAS number.
- Non-volatile content with its test method, and viscosity with spindle, speed and temperature.
- D4/D5/D6 content in ppm, with the analytical method, for EU-bound volume.
- Carrier grade: cosmetic-grade isododecane (typically 99%+ C12 branched) versus industrial grade; colour and odour limits.
- Odour and colour on the neat gel, and a retained sample per lot - the carrier governs both.
For details on how the linear silicone fluids behind these gels behave at different viscosities, see our dimethicone viscosity grade guide.
Quick selection
- Transfer-resistant matte lip or long-wear foundation, EU market: isododecane-carried dimethicone crosspolymer gel.
- Oil-phase thickening, cushion and hot-fill processing: dimethicone-carried dimethicone crosspolymer gel.
- Water resistance and pigment hold in a volatile carrier: acrylates/polytrimethylsiloxymethacrylate copolymer in isododecane.
- Legacy D5-based matte gel: reformulate now if any of the volume ships to the EU.
Shanghai Better Chemical supplies the full elastomer gel set - Isododecane (and) Dimethicone Crosspolymer (CAS 31807-55-3; 213629-14-2), Dimethicone (and) Dimethicone Crosspolymer (CAS 9006-65-9; 63148-62-9), Cyclopentasiloxane (and) Dimethicone Crosspolymer (CAS 541-02-6; 63394-02-5) and Acrylates/Polytrimethylsiloxymethacrylate Copolymer (and) Isododecane (CAS 31807-55-3), with the emulsifying elastomer PEG-10 Dimethicone (CAS 68937-54-2) when the gel has to bridge into a water phase - plus lot-specific non-volatile content, viscosity data and residual cyclics declarations. Tell us the carrier, the viscosity band and the target market and we will quote the grade that clears your regulatory window.