Dimethicone in Hair-Care Formulation: Conditioners, Serums & Grades

You spec “dimethicone” for a rinse-out conditioner, the bench panel signs off, and four months later the same complaint keeps landing on the returns desk: the formula “stops working,” the hair reads limp and dull by the fourth wash. Nothing went wrong with the chemistry. The fluid laid down a film, the film kept layering, and a lighter grade would not have stacked the same way.

Run the opposite play — swap to a water-soluble silicone to dodge the build-up — and the slip the panel approved thins out at the rinse. Same backbone chemistry, opposite behavior in the bottle, and the variable that decides it is one you can read straight off the spec sheet: viscosity grade and water solubility. For a formulator or a buyer cutting the purchase order, those two lines matter more than the INCI name they share.

The short version: Dimethicone (CAS 9006-65-9) is polydimethylsiloxane (PDMS), a linear silicone fluid sold by viscosity grade in centistokes (cSt) at 25 °C, with stocked grades running from about 5 cSt to 1,000,000 cSt and gums above that. As a formulation ingredient it is a film-forming, conditioning, and emollient agent: it spreads a thin hydrophobic film over the cuticle that lowers combing friction (slip) and evens the optical surface (gloss). Higher grades (roughly 1,000–60,000 cSt) deposit a heavier, more durable film with more slip and a stronger tendency to accumulate; low grades (5–50 cSt) are lighter and rinse cleaner. Plain dimethicone is water-insoluble and layers across washes unless the paired surfactant lifts it; water-soluble grafts such as PEG-12 dimethicone rinse far more cleanly and contribute a lighter film. Grade and solubility, not the shared name, drive the result in the bottle.

What dimethicone is, and which grade you are specifying

Dimethicone (CAS 9006-65-9) is polydimethylsiloxane, a linear silicone polymer built from a repeating unit of alternating silicon and oxygen atoms with two methyl groups on each silicon. The INCI name is Dimethicone, and the same material shows up on supplier price lists as dimethyl silicone, dimethylpolysiloxane, or plain “silicone fluid.” In the RawSource catalog it sits in the silicone fluids and oils family and carries conditioning, emollient, and defoaming roles across beauty and personal care, household cleaning, and textiles.

The number that decides a hair-care order is viscosity. Dimethicone is sold by grade, and the grade is its kinematic viscosity in centistokes at 25 °C. A “350 cSt” grade flows at 350 cSt; a “60,000 cSt” grade is a slow, honey-thick fluid. Two drums labeled “dimethicone” with different cSt numbers behave like different raw materials in a conditioner, so the grade, not just the name, belongs on the purchase order and on the bill of materials line.

Chain length is the lever behind the grade. The longer the siloxane backbone, the higher the viscosity and the more substantive the film it leaves at a given dose. That single structural variable, the degree of polymerization, is why one INCI name covers a fluid you can spray and a near-solid gum, and it is why the catalog logs dimethicone as both a defoamer and an emollient: the molecule that lubricates a cuticle is the same one that collapses foam films in a process tank. For the polymer-chemistry background, see what polydimethylsiloxane (PDMS) is.

The viscosity-grade landscape

Grade selection is the first formulation decision and the first sourcing decision. Low grades spread fast and resist rinsing poorly; high grades deposit a thicker, more durable film with more slip and more optical gloss, and a stronger tendency to accumulate. The table maps the common ladder to hair-care formats.

High-viscosity fluids and gums are hard to handle neat, so they often arrive as a pre-made dimethicone emulsion (a separate INCI, with emulsifier and water already in the package) or pre-blended in a volatile carrier. That changes your active-silicone math, your preservative needs, and your cost per kilogram of delivered silicone. Confirm whether a quote covers neat fluid or an emulsion before you compare prices, because the two are not interchangeable on a deposition basis.

Format dictates the carrier as much as the grade does. A leave-on serum usually pairs a low-to-mid dimethicone with a volatile silicone or a light ester so the blend spreads, the carrier flashes off, and the conditioning film is what remains. A rinse-out conditioner suspends a higher grade or an emulsion in a cationic-surfactant base that helps the silicone deposit as the product is rinsed. The grade sets the ceiling on performance; the carrier and base decide how much of that ceiling reaches the fiber. For the full centistoke ladder across silicone fluids, see the silicone oil viscosity guide.

How the film behaves on the fiber

Deposition is a surface effect, not a reaction with the keratin. Dimethicone spreads into a thin, continuous, hydrophobic film over the cuticle. Silicone has low surface tension and a flexible Si–O backbone, so the film wets the irregular cuticle surface and lays down evenly where a fatty oil would bead into droplets. Everything a procurement spec can tie to performance flows from that film.

The film does three measurable things, all of them physical. It lowers friction between fibers and against the comb, which the panel records as easier wet and dry combing slip and detangling. It fills and evens the surface texture optically, presenting a more uniform reflective surface so light scatters less, which the eye reads as gloss. And it leaves a smoother, softer sensory feel on the dry strand. The cured film is also hydrophobic and low in surface energy, which is why it resists plain-water rinsing and tends to reduce the charged, static feel during combing.

Grade drives how much of each property you get. A 50 cSt fluid in a leave-in serum delivers slip and gloss at a barely-there weight. A 5,000 cSt fluid in a mask lays down a thicker cushion that survives rinsing and stays detectable after drying. That is also the central trade-off in the chemistry, and the one behind the complaint at the top of this guide: more film means more slip and gloss and more potential to accumulate. There is no grade that maximizes durable slip and minimizes build-up at the same time, so you pick the side of that line your format needs and design the rest of the system around it.

Wash-off versus leave-in: build-up and water-soluble silicones

“Build-up” is the word your end users reach for, and it has a precise cause. Plain dimethicone is water-insoluble. It does not rinse away in plain water and only partly lifts off with a mild surfactant, so each wash-and-condition cycle can leave a little more silicone on top of what is already there. On fine or low-porosity hair, that layered film weighs the strand and dulls the gloss, the failure mode that reads downstream as “the conditioner stopped working.”

Two formulation levers manage it. The first is the surfactant system in the paired shampoo: an anionic (for example sulfate) surfactant at an adequate level lifts deposited silicone, while a mild, sulfate-free cleanser may leave it behind. The second is choosing a removable silicone. Water-soluble silicones carry polyethylene-glycol grafts on the same PDMS backbone, which makes them water-dispersible and far easier to rinse. PEG-12 dimethicone (CAS 68937-54-2) is the common example: it contributes a lighter film than plain dimethicone and does not stack across repeated washes.

So the wash-off versus leave-in decision is really a solubility decision. If durable slip and gloss on coarse or color-treated hair is the brief, plain dimethicone at a mid-to-high grade is the workhorse, and you design the partner shampoo to clear it. If the brief is a daily-use, lightweight, low-build conditioner or a clarifying-compatible line, a water-soluble grade or a low-cSt fluid does more for the formula than the heaviest fluid on the shelf.

Amodimethicone and phenyl trimethicone: when to reach for a modified silicone

Two modified silicones change the deposition or the optics without the build-up profile of a heavy plain fluid. Amodimethicone is an amine-functional silicone: its cationic amine groups give it affinity for the higher-charge, anionic regions of weathered or chemically processed cuticle, so deposition is directed toward those sites and accumulates less elsewhere. That charge-directed substantivity is a physical-chemistry property of the molecule, not a treatment of the hair, and it is why amodimethicone is a frequent pick where selective deposition matters.

Phenyl trimethicone is the other fork. Substituting phenyl groups onto the backbone raises the refractive index, so the film contributes more optical gloss at a lighter feel than an equivalent plain dimethicone. Each of these is a separate INCI and CAS line on the bill of materials, so quote them as distinct raw materials rather than drop-in substitutes for the plain fluid. Where the brief is simply heavier slip and a durable film, a mid-grade plain dimethicone or a 1,000 cSt silicone oil is the more economical starting point.

What to question on the certificate of analysis

Treat the Certificate of Analysis (CoA) and Technical Data Sheet (TDS) as the contract, not the marketing copy. Five lines decide whether a lot is fit for a hair-care formula.

1. Viscosity grade and tolerance. Confirm the cSt value at 25 °C and the allowed band. A grade that drifts changes deposition and feel across lots; a wide or unstated tolerance is a quality-control gap, not a rounding detail. 2. Residual cyclic siloxanes (D4, D5, D6). Linear dimethicone can carry leftover cyclic monomer from manufacturing. The EU caps D4 and D5 at 0.1 percent by weight in wash-off cosmetics, so ask for the residual figure in ppm and check it against that limit before committing a wash-off formula. 3. Water and volatiles. Free water in a neat fluid points to a handling or storage problem and can seed downstream microbial issues. For an emulsion grade, confirm the declared water content and the preservative system instead. 4. Exact INCI and CAS identity. “Dimethicone” the fluid (CAS 9006-65-9) is not dimethicone crosspolymer, not a copolyol, and not a copolymer. A shared or vague CAS on the sheet is a red flag; match the INCI grade to your formula line item. 5. Appearance and clarity. Cosmetic-grade dimethicone should be a clear, colorless fluid free of haze and particulates. Color or turbidity signals contamination or an off-spec lot, so reject on it rather than blend it in.

Grades, specs, and bulk sourcing

Dimethicone fluids ship in pails, drums, and IBC totes for the pourable grades, with neat high-viscosity fluids and emulsions usually moving in drums. Specify the grade, the pack size, and whether you need neat fluid or an emulsion before you compare quotes, because those choices move both the price per kilogram of active silicone and the handling on your dock.

Four variables move the landed cost more than the spot silicone price. Viscosity grade comes first, since the highest grades and gums cost more to produce and handle. A tight residual-cyclics specification is second: a low D4/D5 limit narrows the supplier pool and lifts the price. Packaging and order size set the third lever through freight and minimum-run economics, and origin sets the fourth through transit time and customs clearance on imported versus domestic supply. Hold the same grade and the same residual-cyclics spec across competing quotes so you are comparing like for like, not pricing a looser material against a tighter one.

RawSource quotes dimethicone by viscosity grade for bulk RFQ, with domestic US stock on common grades and global sourcing where a tighter residual-cyclics or identity spec is required. The dimethicone product page lists the grades available, and the Beauty & Personal Care hub collects the related conditioning silicones, including the water-soluble and phenyl-modified options, for side-by-side specification. Send the target grade, the residual-cyclics limit, your wash-off or leave-in format, and the pack size, and request a sample to qualify deposition and feel on your own base.

Regulatory check

Dimethicone is one of the better-documented silicones for personal-care use, which helps a procurement file even though most of that documentation sits outside hair care. In the United States, dimethicone is recognized as an OTC skin-protectant active at 1 to 30 percent under the FDA monograph at 21 CFR 347.10; that status governs skin-protectant drug claims and is not a hair-care permission or a claim RawSource makes, but it signals a long regulatory track record for the polymer. Dimethylpolysiloxane is also a permitted defoaming agent in food processing under 21 CFR 173.340, again evidence of an established dossier rather than a direct hair-care endorsement.

The live compliance issue for cosmetics is the residual cyclic siloxane content above. The EU restricts D4 and D5 to 0.1 percent by weight in wash-off cosmetic products through REACH Annex XVII, introduced by Commission Regulation (EU) 2018/35, and the scope has since been extended toward D6 and leave-on products. Even for US-only sales, writing the 0.1 percent residual-cyclics line into your specification future-proofs the formula and keeps export options open. For substance identity and synonym confirmation, the dimethicone entry on PubChem is a useful primary cross-check against a supplier’s INCI claim. The Cosmetic Ingredient Review (CIR) Expert Panel has also published an assessment of dimethicone and the wider siloxane family used in cosmetics, which gives a regulatory-affairs lead a documented reference to attach to a product dossier rather than a supplier assurance alone.

Frequently asked questions

Which dimethicone viscosity grade should I use for a conditioner versus a serum?

For a leave-on serum, a low grade in the 5 to 50 cSt range spreads fast and leaves a light film with minimal residue, usually paired with a volatile carrier. For a rinse-out conditioner, a mid-to-high grade (1,000 to 5,000 cSt) or a dimethicone emulsion deposits a heavier, more durable film with more slip and gloss out of a cationic base. The grade sets the ceiling; the carrier and base decide how much of it reaches the fiber.

Dimethicone or amodimethicone — which deposits more selectively?

Amodimethicone deposits more selectively. Its cationic amine groups give it affinity for the higher-charge, anionic regions of weathered or chemically processed cuticle, so it concentrates there and accumulates less on the rest of the strand. Plain dimethicone deposits a more uniform hydrophobic film and, at higher grades, has a stronger build-up tendency. They are separate INCI and CAS materials, so spec them as distinct line items.

What is the difference between wash-off and leave-in dimethicone behavior?

It comes down to water solubility. Plain dimethicone is water-insoluble: in a leave-in it stays on the fiber and in a wash-off it resists plain-water rinsing and can layer across cycles unless an anionic surfactant lifts it. Water-soluble grafts such as PEG-12 dimethicone are water-dispersible, rinse far more cleanly, and contribute a lighter film, which suits daily-use and low-build formats.

How do I avoid silicone build-up in a formula?

Three levers. Drop to a lower viscosity grade or a water-soluble silicone (for example PEG-12 dimethicone) so less film persists per cycle; pair the conditioner with a shampoo whose surfactant system lifts deposited silicone; or switch to amodimethicone for charge-directed deposition that accumulates less on undamaged lengths. Decide the wash-off versus leave-in target first, then pick the grade to match.

How do I source dimethicone in bulk, and what should be on the spec?

Specify the viscosity grade and tolerance at 25 °C, whether you need neat fluid or an emulsion, the residual-cyclics limit (the EU 0.1 percent D4/D5 cap is the common reference), the INCI/CAS identity, and the pack size (pails, drums, or IBC totes). Hold those constant across quotes so you compare like for like, and request a sample to qualify deposition and feel on your own base before committing a lot.

Editorial note. This article is general technical and formulation guidance for hair-care formulators and procurement professionals. It describes dimethicone’s formulation function and physical and sensory properties; it makes no medical, health, cosmetic-efficacy, or hair- or scalp-health claims. Deposition, feel, build-up, and rinse behavior depend on your specific grade, dose, carrier, surfactant system, and substrate, and must be validated on your own formula; the Certificate of Analysis governs the grade you buy. Regulatory thresholds are cited from the US Code of Federal Regulations (eCFR) and EU REACH Annex XVII as published, and must be confirmed for your application and jurisdiction. Products are sold for industrial and professional use only. RawSource makes no warranty, express or implied, and assumes no liability for use of this information.