Brassica Oil Copolymer

Overview

Brassica oil copolymer (sometimes sold under the name PlantSil, Plant-Silica, or as a generic “plant-derived silicone alternative”) is a polymerised oil made from the seed oils of plants in the Brassica family — rapeseed, mustard, and related crops. The starting fatty acids are catalytically polymerised and hydrogenated to produce a clear, viscous, almost odourless liquid that behaves remarkably like a silicone.

In feel, it is closest to a low-viscosity dimethicone — slick, smooth, fast-spreading, with a soft dry finish. It is one of the more credible silicone alternatives for makers who need a true silicone-replacement in a “100% plant-derived” formula.

Suppliers sell different molecular weights under similar names. Lower MW versions feel light; higher MW versions add slip and structure. Some products are 100% brassica copolymer; others are blends of the copolymer with squalane, ester, or polydecene.

Shelf life is 2-3 years.

What it does in a formula

• Silicone-style slip — the defining feature
• Dry-touch finish — sinks in and leaves a satin rather than oily feel
• Spreading agent — helps other oil-phase ingredients distribute evenly
• Solubilises waxes and pigments — useful in makeup and sticks
• Hair conditioning — gives the same smooth-cuticle feel as dimethicone without the build-up concern

It does not deliver skin-care benefits on its own. It is a structural and feel ingredient.

How to use

Add to the oil phase. Heat-stable up to 100 C, so emulsification at 70-75 C is fine.

Usage rates by product type:

• Face creams and lotions: 3-8%
• Primers and makeup: 5-15%
• Body lotions: 3-8%
• Hair conditioners and serums: 2-8%
• Lipsticks and lip glosses: 5-15%
• Sunscreens: 3-10%
• Stick products: 3-10%

For a silicone-free face cream that wants the silicone feel, 5% brassica oil copolymer + 3% squalane + 2% isoamyl laurate gives a clean, light, smoothing finish.

Best for / Worst for

Best for: plant-based and natural-positioned face creams, silicone-free primers, hair conditioners marketed without silicones, COSMOS-eligible formulations, customers who specifically avoid dimethicone.

Worst for: budget formulating (it is more expensive than dimethicone), formulations that need the precise viscosity tuning that dimethicone offers (brassica copolymers come in fewer grades), heavy occlusive balms (it is too light).

Common pitfalls

Expecting an exact dimethicone clone. It is close, but not identical. The dry-touch finish is slightly different — a tiny bit more “vegetable oil” character. Most customers will not notice, but if your formula needs the precise silicone feel, you may need to layer two silicone alternatives (brassica + isododecane, for example) to match it fully.

Buying without checking the spec. Different suppliers sell very different molecular weights and viscosities under similar names. Always ask for the viscosity range and the recommended usage rate before reformulating.

Treating it as a moisturiser. It is a structural and feel ingredient, not a moisturiser. Pair with humectants and occlusives.

Substitutes

• Dimethicone (if silicones are acceptable) — closest match for feel.
• Hydrogenated polydecene — synthetic but plant-derived alternative, similar role.
• Isoamyl laurate — natural, simpler chemistry, lighter feel.
• Coco-caprylate — natural, slightly less silicone-like feel.
• Squalane — different feel (slick rather than dry-touch), but plant-derived.