If white mineral oil is the formulator's first basic oil, dimethicone — linear polydimethylsiloxane, INCI Dimethicone, CAS 63148-62-9, polymer formula (C₂H₆OSi)ₙ — is the second. It is the slip in your conditioner, the matte veil in your foundation, the protective film in your sunscreen, the antifoam in your fermentation tank, and the mould-release spray on your rubber press. Yet buyers routinely pick the wrong grade because the number on the drum — 50, 350, 500, 1000, 1500 cSt — is read as a price signal rather than as the single most important functional specification. This guide walks through what cSt actually means, how the ladder maps to applications across personal care, plastics and food, and the COA specs that distinguish cosmetic-grade from industrial-grade material.
What the cSt number measures
The number in Dimethicone 350 is kinematic viscosity at 25 °C in mm²/s (centistokes), measured per a capillary or rotational method. Mechanically, dimethicone 50 pours like a lightweight oil, 350 flows like a facial serum, 500 has a noticeable body, 1000 is a slow ribbon, and 1500 is a viscous film former. The same chemistry, the same CAS number, the same INCI declaration — only the polymer chain length (and the average molecular weight, roughly 3,000 Da at 50 cSt to ~18,000 Da at 1500 cSt) differs. So the cSt number is your first and best purchasing filter: within one product family, formulators standardize on a viscosity band and stay there.
One CAS, two regulatory families
All cosmetic and industrial grades of linear dimethicone in our range carry CAS 63148-62-9, but that single number covers two very different supply chains:
- Cosmetic / personal-care grade — tightly controlled cyclic content (D4 – D6 siloxanes — the small-ring cyclomethicones — typically < 0.1% combined), low volatile matter (loss at 150 °C typically < 0.3%), heavy metals and catalysts near detection limits, residual HCl below 5 ppm. Backed by INCI declaration, safety dossier support and (for EU) the relevant SCCS opinion on D4/D5/D6 use.
- Industrial grade — the same polymer chemistry but looser cyclic and volatile limits, no cosmetic dossier support. Right for rubber mould release, plastics lubrication and general defoaming where skin exposure is incidental.
For food use, dimethicone 100 food grade (E900) is manufactured to FDA 21 CFR 173.340 (and EU E900), with the antifoam use levels explicitly listed. The cosmetic-grade drum and the food-grade drum should never be cross-shipped: the documentation gap is the issue, not the chemistry.
Viscosity selection by application
| Viscosity grade | Personal-care use | Industrial / food use |
|---|---|---|
| 50 cSt | Lightweight lotions, serums, hair conditioners, detangling sprays, antiperspirant roll-ons — fast-spreading, non-greasy slip, no occlusive feel | Process antifoam (diluted emulsion), textile fibre lubrication |
| 100 cSt food grade (E900) | Not typical for leave-on skin care (E900 documents are food-only) | Food antifoam in fermentation, jam and fry-oil processing; release agent in baking (FDA 21 CFR 173.340 levels) |
| 350 cSt | The workhorse band — emulsions (skin care, sunscreen), shampoo and conditioner systems, colour cosmetics; balanced spread and slip | Plastic mould release, rubber processing aid, polish and cleaner formulations |
| 500 cSt | Face creams, primers and foundations, hair serums — medium-high viscosity, soft-focus optical effect | Release agent for cast polyurethane, anti-block slip for polyolefin films (speciality blends) |
| 1000 cSt | Rich skin creams and lotions, sunscreen water-resistance systems, hair conditioners — conditioning film, better pick-up | High-viscosity mould release, hydraulic damping fluids |
| 1500 cSt | Barrier creams, night creams, hand and body protectants, hair glossers and pomades — the most occlusive, film-forming grade | Grease compounding, high-viscosity damping, vacuum pump oils |
Two practical points worth more than the table. First, viscosity predicts spread and slip, but not optical effect: a 500 cSt dimethicone can be tuned to a soft-focus matte finish or a glossy slip by blending with a low-viscosity carrier and pigments. Second, in emulsions, dimethicone raises skin feel but contributes nothing to emulsion stability — that burden still sits with the primary emulsifier system, so always pilot with your actual surfactant package and not at a single point.
COA specs that decide cosmetic from industrial
- Kinematic viscosity at 25 °C — must sit in a narrow band around the stated grade (typically ±10%); wide bands are the first sign of blended lots and batch-to-batch drift.
- D4–D6 cyclic content — the small-ring siloxanes that are the subject of EU regulatory pressure (D4/D5 restricted under REACH, D6 under watch). Cosmetic-grade COAs must report each; food-grade E900 must meet the same low limits. Industrial grade is not held to this.
- Volatile matter (loss at 150 °C / 24 h) — high volatility in a high-cSt oil means chain-length drift and "drying out" of finished products; cosmetic grade should be well under 0.5%, food-grade similar.
- Specific gravity and refractive index — quick identity checks: ~0.94–0.97 g/cm³ and ~1.40 RI across the cSt range; a sample that is off-spec here is contaminated.
- Flash point (open cup) — from ~200 °C at 50 cSt to ~315 °C at 1000 cSt; very low flash on a high-cSt sample signals a contaminated drum.
- Heavy metals, residue on ignition, HCl — cosmetic/food must report near-zero; industrial can be looser.
Dimethicone vs. white mineral oil — picking one, or combining
Both are basic oils, but they are not interchangeable. Dimethicone is fully synthetic, water-clear, odourless, oxidation-proof and breathable; white mineral oil is a refined petroleum distillate with a faint hydrocarbon character and a tendency to yellow on aging. In skin care, dimethicone wins on feel (slip, matte optical, no greasiness) and on barrier performance per gram; white mineral oil wins on cost and on regulatory familiarity in mass-market formulations. In hair care, dimethicone is the conditioning backbone; mineral oil is rare. In plastics and rubber, both compete in mould release, with dimethicone preferred when staining and high-temperature stability matter, mineral oil preferred when cost dominates.
Sampling and procurement practice
Dimethicone is technically a commodity, but cosmetic-grade lots vary noticeably in cyclic content and feel. The procurement workflow that avoids the common traps: shortlist by the actual cSt grade and the actual grade claim (cosmetic or E900 food), reject any COA missing the D4–D6 line, run a side-by-side feel panel of 350 cSt against your incumbent at the same loading, and ask for per-lot COAs — not a one-time spec sheet. For food applications, confirm the E900 documentation and the use level is within 21 CFR 173.340 or the local equivalent. For plastics or rubber, an industrial-grade drum is acceptable, but state the intended end-use to your supplier so they can recommend the right viscosity and packaging.
Shanghai Better Chemical supplies the full 50, 350, 500, 1000 and 1500 cSt cosmetic-grade dimethicone ladder (CAS 63148-62-9, INCI Dimethicone, China origin), as well as 100 cSt food-grade E900 for antifoam and release use. Per-lot COA, D4–D6 data, and TDS/INCI documentation supplied. Tell us your application, target viscosity and grade, and we will recommend the right dimethicone and quote current pricing.