When a supplier says “dimethicone,” many buyers picture one fixed material. It is not. The same silicone chemistry comes in two very different shapes — long linear chains and small cyclic rings — and those two shapes behave nothing alike, especially in the eyes of cosmetics regulators. This guide explains the difference in plain language, why the cyclic form (D4/D5/D6) is restricted, and what real batch testing shows for our W201 cosmetic-grade dimethicone.
Linear vs cyclic: the one-minute version
Silicone molecules are built from the same few elements — silicon, oxygen, carbon and hydrogen. The difference is their shape.
- Linear dimethicone is a long, open chain, like a strand of cooked spaghetti. Dimethicone (INCI name, CAS 9006-65-9) is this linear form. Our W201 is a linear dimethicone.
- Cyclic siloxanes are small, closed rings, like tiny bracelets. The three you hear about are D4, D5 and D6 (octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane and dodecamethylcyclohexasiloxane).
Both are “silicone,” but a long chain and a small ring spread, evaporate and interact with skin in completely different ways. The chain length of the linear form is what decides viscosity — that is the 5 to 1000 cSt range you see in W201 grades.
Why the rings get all the regulatory attention
The small rings are volatile — they evaporate easily — and they persist in the environment. That is why regulators limit them, while linear dimethicone is not in those restrictions.
In the EU, wash-off cosmetics have been limited to 0.1% (1000 mg/kg) D4 and D5 since 2020, and Regulation (EU) 2024/1328 extends the restriction to D4, D5 and D6 across cosmetic categories, with the final deadline of 6 June 2027. In ASEAN, D4 is now prohibited under ACD Annex II and Vietnam has already recalled products on D4 grounds — see our D4/D5 compliance guide for the full timeline.
Put simply: linear dimethicone is the stable, non-volatile workhorse; the cyclic form is what the rules are written about.
How W201 is made — and why it stays linear
W201 starts from virgin, first-use silicone feedstock — not cracked or recycled material — processed with high-purity water. The controlled reaction builds linear polymer chains and keeps any residual rings down to a trace.
This matters because the cheap route uses cracked or reclaimed siloxane, which carries more residual cyclics and impurities. Starting from virgin material is the reason W201 can ship with such low D4/D5/D6 numbers, and every batch is released against a specification with a batch test report.
The real numbers: what testing shows
A recent batch of W201 was analysed for cyclic siloxanes by GC-MS (SGS laboratory method). The results, in mg/kg (where 1 mg/kg = 0.0001%):
| Substance | Result (mg/kg) | As percentage | EU limit |
|---|---|---|---|
| D4 | 70.8 | 0.0071% | 0.1% = 1000 mg/kg |
| D5 | 6.2 | 0.0006% | |
| D6 | 7.8 | 0.0008% |
Batch test report, GC-MS (SGS laboratory method). For context, 0.1% equals 1000 mg/kg, so the D4 result of 70.8 mg/kg sits roughly 14 times below the limit — and the three together total about 85 mg/kg, around one-eighth of the 0.1% threshold.
Three questions to ask your supplier
If a supplier offers “low-cyclics dimethicone,” the claim is only worth something with data behind it. Ask three things:
- Show the COA with D4/D5/D6 in mg/kg, tested by GC-MS. If a supplier cannot show this, assume the worst.
- Ask whether the feedstock is virgin or cracked/recycled. Virgin feedstock (W201) is what keeps residual rings to a trace.
- Compare the number to 1000 mg/kg (0.1%). Anything comfortably under — like W201’s 70.8 mg/kg D4 — is well inside the limit.
Choosing a silicone partner is easier with the full picture. For how chain length (viscosity) shapes the feel, read our cosmetic-grade dimethicone viscosity guide. For the W201 grade range itself, see our silicone fluids range.
FAQ
Is dimethicone a cyclic siloxane?
No. Dimethicone is a linear silicone polymer (polydimethylsiloxane, PDMS). D4, D5 and D6 are cyclic siloxanes — small rings. They share the same elements but have very different shape, volatility and regulatory status.
What is the legal limit for D4, D5 and D6 in cosmetics?
In the EU, wash-off cosmetics have been limited to 0.1% (1000 mg/kg) D4 and D5 since 2020, and Regulation (EU) 2024/1328 extends the restriction to D4, D5 and D6 across cosmetic categories, with the final deadline of 6 June 2027. ASEAN has prohibited D4 under ACD Annex II.
How much D4, D5 and D6 is in W201?
A recent W201 batch tested by GC-MS (SGS laboratory method) showed D4 70.8 mg/kg, D5 6.2 mg/kg and D6 7.8 mg/kg. Each is far below the 1000 mg/kg (0.1%) threshold, with D4 sitting about 14 times under the limit.
Does low-cyclics change how dimethicone feels?
No. The feel of dimethicone comes from chain length — its viscosity — not from residual rings. The 5 to 1000 cSt W201 range is about chain length; see our viscosity guide for the map.