Silicone gum is an ultra-high-molecular-weight polydimethylsiloxane (PDMS) — a stiff, gum-like silicone polymer that does not pour or flow at room temperature. With a molecular weight in the high hundreds of thousands to several million, it is the raw base polymer behind high-consistency (HCR/HTV) silicone rubber, silicone pressure-sensitive adhesives, antifoam compounds, and high-performance hair and skin conditioners. It sits between thin silicone fluids and finished silicone rubber: heavier and more elastic than any pourable oil, yet uncrosslinked and not an elastomer until it is compounded and cured.
What Is Silicone Gum?
Silicone gum is the same dimethylsiloxane backbone you find in ordinary silicone oil, taken to a far higher degree of polymerization. A 350 cSt silicone fluid might have a few hundred siloxane repeat units; a gum carries thousands. That difference in chain length is everything. As the chains grow, entanglement between them increases sharply, and the material crosses from a viscous liquid into a soft, cohesive, non-flowing solid that we call a gum. Push a thumb into it and it deforms slowly and springs partway back. Leave it on a bench and it holds its shape rather than spreading into a puddle the way an oil does.
The practical consequence for a compounder is that gum has to be milled, banded on a two-roll mill, or worked in a kneader rather than pumped. You cannot meter it like a fluid. End-group (chain-terminating) chemistry is the second variable that defines a grade. Silanol (hydroxyl)-terminated gums carry reactive –OH groups at the chain ends and are the workhorse for condensation-cured systems and for many antifoam and personal-care blends. Vinyl-terminated (and vinyl-on-chain) gums provide the cure sites for addition (platinum) cure used in most modern HCR rubber. Trimethyl-terminated, or non-reactive, gums are end-capped and inert, used where you want the high molecular weight without participating in a crosslink — film-formers and certain PSA and antifoam roles. When you specify a gum, the end group matters as much as the molecular weight.
Silicone Gum vs. Silicone Fluid vs. Silicone Rubber
The three are routinely confused on RFQs because they share a chemistry and a name. They are not interchangeable. The table below is the fastest way to place a material in the right category.
| Property | Silicone Gum | Silicone Fluid / Oil | Silicone Rubber |
|---|---|---|---|
| Form / consistency | Stiff, tacky, gum-like mass | Pourable liquid, thin to syrup-thick | Solid, resilient elastomer |
| Molecular weight | Very high (~hundreds of thousands to millions) | Low to moderate (hundreds to tens of thousands) | Crosslinked network (effectively infinite) |
| Flows at room temperature? | No — essentially non-flowing | Yes | No |
| State | Uncrosslinked raw polymer | Uncrosslinked liquid polymer | Crosslinked, cured product |
| Typical role | Base polymer for rubber, PSAs, antifoam, conditioners | Lubricant, carrier, release, defoamer fluid, conditioner | Finished part: seals, gaskets, tubing, molded goods |
Read the table as a process sequence, not just a comparison. A gum is the input; rubber is the output after you add filler, additives, and a cure system and apply heat. A fluid is a different product class entirely — it stays liquid by design and is never meant to become an elastomer. Mixing up gum and fluid on a purchase order is a common and expensive error: a kneader-grade gum will not behave like a metered fluid, and a defoamer fluid will not band on a mill.
Forms and Grades
Silicone gum ships in two broad commercial forms, and the right one depends on how your line handles material.
Raw gum
Neat, high-consistency polymer supplied in slabs, blocks, or chip form. This is what rubber compounders and PSA formulators buy when they want to control filler loading and additives themselves. It demands milling or kneading equipment and trained handling, but it gives the most formulation latitude.
Gum blends (cut in a carrier)
Many buyers cannot mill a raw gum, so suppliers pre-disperse it in a volatile or low-viscosity carrier. A common personal-care form is a dimethiconol gum dispersed in cyclopentasiloxane (D5) — typically supplied as a pourable or spreadable blend in the range of roughly 10–15% gum, though exact ratios vary by grade. The carrier flashes off or spreads on application and leaves the high-molecular-weight gum behind as a continuous film. Blends trade away some formulation control for drop-in convenience, and you pay for carrier you eventually drive off. For a formulator without mill capacity, that trade is usually worth making.
Across both forms, specify the end group deliberately. Silanol-stopped gums are the default for condensation cure and for silica-filled antifoam compounds, where the –OH groups help anchor and treat the silica. Vinyl-functional gums are required wherever you intend a platinum addition cure. Trimethyl-stopped (non-reactive) gums give you molecular weight and film-forming behavior without a cure handle. A grade that is right for one route is wrong for another, so the end group belongs on the line item, not in a note.
Applications by Sector
High-consistency silicone rubber (HCR / HTV)
This is the single largest use. Vinyl-bearing gum is compounded with reinforcing fumed silica, processing aids, and a cure system, then shaped and heat-cured into elastomer. The result is the tough, temperature-resistant rubber behind extruded profiles, tubing, gaskets, keypads, and molded parts that hold properties from well below freezing to north of 200 C. Gum molecular weight and the silica package together drive tear strength and tensile, so compounders tune both. The trade-off is processing energy: the same high molecular weight that gives mechanical performance is what forces milling and limits throughput.
Silicone pressure-sensitive adhesives (PSAs)
Silicone gum blended with a tackifying MQ silicone resin produces PSAs that hold where organic adhesives fail: high-temperature masking and splicing tapes, electrical and medical tapes, and release applications. The gum supplies cohesive strength and elongation; the resin supplies tack. Adjusting the gum-to-resin ratio is the primary lever between peel adhesion and shear holding power, and the two pull against each other.
Antifoam and defoamer compounds
A silicone antifoam compound is, at its core, a silanol-stopped gum (or high-viscosity fluid) with hydrophobic treated silica dispersed into it. The gum provides the viscous, spreading silicone phase; the silica particles rupture foam lamellae. That compound is then emulsified or diluted into the dosed product. Gum-based compounds are valued for activity at low dose across pulp and paper, fermentation, coatings, textiles, and wastewater. The real-world tension is dispersion and persistence: too coarse and the antifoam underperforms, too fine and it can deplete or cause defects, so silica grade and shear during make-down are tightly controlled.
Personal care — hair and skin conditioning
Dimethiconol is the silanol-terminated, high-molecular-weight silicone gum used widely in hair care. Delivered as a dimethiconol-in-cyclopentasiloxane blend, it deposits a thin, high-molecular-weight film that delivers smooth slip, detangling, frizz control, and shine without the heavy, greasy feel of a fixed silicone oil. The volatile carrier evaporates after application and leaves the conditioning gum on the fiber. Formulators weigh deposition and feel against build-up over repeated use, because the same film persistence that conditions can, dose after dose, accumulate, which is why level and co-surfactant choice matter.
Mold-making and release
High-molecular-weight gum is also used in mold-making compounds and as a component of release systems, where its film-forming character and thermal stability give clean part release and repeatable mold life. Here the gum’s resistance to flow is the asset: it stays where it is placed.
Sourcing Silicone Gum in Bulk
RawSource supplies silicone gum and gum blends in bulk for rubber compounders, adhesive and antifoam formulators, and personal-care manufacturers. Because grade selection drives everything downstream, a useful RFQ specifies four things up front: the end-group chemistry (silanol, vinyl, or trimethyl-stopped), whether you need raw gum or a blend and at what gum percentage and carrier, your annual or per-lot volume, and your documentation requirement (CoA, and any regulatory or compositional statements your application demands). Sending those four with your inquiry lets us match a grade and quote without a round of back-and-forth.
For adjacent silicone chemistries, see the dimethiconol grade often supplied as a personal-care gum blend, very high-viscosity silicone oil 500,000 cSt for applications at the fluid-to-gum boundary, and standard dimethicone fluids. Browse the full silicone fluids and oils category for the pourable end of the range. If you are setting up a new supply line, our guide to chemical procurement walks through spec, qualification, and documentation.
Frequently Asked Questions
What is silicone gum?
Silicone gum is an ultra-high-molecular-weight polydimethylsiloxane (PDMS) — a stiff, gum-like, essentially non-flowing silicone polymer. Its molecular weight runs from the high hundreds of thousands into the millions, far above pourable silicone fluids. It is the uncrosslinked raw polymer that becomes high-consistency silicone rubber after compounding and cure, and it also serves adhesive, antifoam, and conditioning roles.
What is silicone gum used for?
Silicone gum is mainly the base polymer for high-consistency (HCR/HTV) silicone rubber used in seals, tubing, profiles, and molded parts. It is also used in silicone pressure-sensitive adhesives, in silicone antifoam and defoamer compounds (gum plus treated silica), in hair and skin conditioners as a film-forming gum blend, and in mold-making and release systems.
What is the difference between silicone gum and silicone oil?
The difference is molecular weight and consistency. Silicone oil (fluid) is a lower-molecular-weight PDMS that pours and flows like a liquid and is used as a lubricant, carrier, or defoamer fluid. Silicone gum is a much higher-molecular-weight PDMS that is stiff and non-flowing and serves as the raw base for rubber, adhesives, and conditioning films. Same chemistry, very different chain length.
What is the difference between silicone gum and silicone rubber?
Silicone gum is the uncrosslinked raw polymer; silicone rubber is the cured elastomer made from it. Gum is processed — milled with reinforcing silica, additives, and a cure system — then heat-cured to crosslink the chains into a resilient, three-dimensional network. In short, gum is the starting material and rubber is the finished, crosslinked product.
What is a silicone gum blend?
A silicone gum blend is high-molecular-weight gum pre-dispersed in a volatile or low-viscosity carrier, often cyclopentasiloxane (D5) or a light silicone fluid. The carrier makes the otherwise non-flowing gum pourable and easy to formulate. On application the carrier evaporates or spreads and leaves the gum behind as a film. Blends suit buyers who cannot mill raw gum, at the cost of some formulation control.
Is dimethiconol a silicone gum?
Yes. Dimethiconol is a silanol (hydroxyl)-terminated, high-molecular-weight silicone gum. In personal care it is usually supplied as a dimethiconol-in-cyclopentasiloxane gum blend, where it deposits a smooth, non-greasy conditioning film for slip, detangling, frizz control, and shine. It is a representative example of a silanol-stopped gum used outside of rubber compounding.
How is silicone rubber made from silicone gum?
The gum is compounded on a mill or in a kneader with reinforcing fumed silica, processing aids, and a cure system, then formed and heat-cured. Curing crosslinks the gum’s long chains into an elastic network, converting the soft, non-flowing gum into a resilient elastomer. Most modern high-consistency rubber uses vinyl-functional gum with a platinum addition cure; condensation cure with silanol gum is also used.
