Silicone Rubber Supplier for Molders

The short answer

Silicone rubber is the pick when a soft part has to work across a wide temperature range, keep its seal when hot, or come with a long medical or food-contact record. It is a thermoset: it cures in the mold and cannot be remelted, so scrap and process rules differ from TPE or TPV. The things that most often go wrong are flash on LSR tools and cure inhibition from contamination.

Silicone grade types

Two-part liquid silicone rubber (LSR) for injection molding
High-consistency rubber (HCR), a gum for compression and transfer molding and extrusion
Fluorosilicone grades for fuel and oil contact
High-tear grades for thin flaps, valves and membranes
Grades tested for medical uses, and food-contact grades
Self-bonding LSR for two-shot molding onto thermoplastics
Optically clear, low compression set, flame-retardant and self-lubricating grades

About silicone rubber

Silicone rubber is a thermoset elastomer built on a silicon-oxygen backbone instead of the carbon chain of most plastics and rubbers, usually reinforced with fumed silica. That backbone is why it stays flexible well below freezing, keeps working near 200°C / 392°F, holds a low compression set across that range and shrugs off UV and ozone. Unlike the other materials on this site, it is not a pellet: it arrives as a two-part liquid or as a gum, cures in a hot mold or oven, and cannot be remelted. Its weak points are tear strength in standard grades, swelling in fuels and many oils, and cost. Silicone rubber grades differ widely by type, cure system and documentation, so tell us which type you run.

Common applications

High-heat seals and gaskets for ovens, cooktops, lighting and appliances
Medical tubing and non-implant device parts
Baby products, kitchenware and bakeware
Keypads and soft-touch buttons
Valves, diaphragms and membranes
Extruded tubing, cord and profiles
Connector seals and electrical insulation parts

Typical properties

Hardness	About 10A to 80A; gels softer (Shore OO scale)
Service temperature	About −55 to 200°C / −67 to 392°F; special grades higher
Density	About 1.1–1.2 g/cm³ (LSR); filled grades higher
Tear strength	Low in standard grades; high-tear grades much better, but usually below TPV or TPU at a similar hardness
Compression set	Very good over a wide temperature range
Chemical and oil resistance	Good in water; excellent UV and ozone resistance; swells in fuels, many oils and hydrocarbon solvents (fluorosilicone grades resist fuels and oils better)
Clarity	Translucent to water-clear (LSR); easy to pigment
Relative cost	Higher per pound than TPV, TPE or flexible PVC

Property ranges are general guidance and vary by grade and supplier; a polymer chemist confirms the exact spec against the data sheet and COA for your application.

Which grade to ask for

Name the type you run (two-part liquid or gum), the cure system, the hardness and any documents the part needs.

Grade type	Use it for	Watch out for
LSR, general purpose (two-part, platinum-cured)	High-volume injection-molded seals, valves, keypads, baby and kitchen parts	Very low viscosity, so it needs tight tools and meter-mix equipment. Platinum cure is sensitive to contamination
HCR (gum), peroxide- or platinum-cured	Compression and transfer molded parts, extruded tubing, profiles and cord	Peroxide-cured parts usually need a post-cure. Catalyzed compound has a limited shelf life
High-tear grades	Thin flaps, membranes, valves and parts stretched over edges	Usually still below TPU or TPV at a similar hardness. Compare tear values by the same test method
Fluorosilicone	Seals and diaphragms that see fuel, oil or solvent	Costs considerably more than standard silicone, and its top-end heat rating is typically lower
Medical-test and food-contact grades	Non-implant device parts, tubing and seals; food equipment and kitchenware	Documents are grade-specific: ISO 10993 or USP Class VI reports, or the producer’s FDA letter. Implant uses are a separate category
Self-bonding LSR	Two-shot or insert molding onto thermoplastic substrates	The bond depends on the substrate grade, and the substrate must handle the hot mold. These grades can also stick to the tool
Specialty LSR: optically clear, low compression set, flame-retardant, self-lubricating (oil-bleed)	Lenses and light guides, hot seals, electrical parts, connector seals	UL recognition is grade-specific and color-specific; check the grade’s listing on UL Product iQ. Oil-bleed grades can hurt bonding and printing

Typical starting points. Grades vary, so confirm on the data sheet for the exact grade.

Processing notes

No drying needed. Silicone is not a pellet and is not dried. Keep containers sealed and in date: LSR and catalyzed HCR have a shelf life, so check it before you open a pail or drum.
Metering and mixing (LSR). The two parts, most often mixed 1:1, are pumped from pails or drums through a meter-mix unit and a static mixer, with pigment added there if needed. The barrel and cold runner are kept cool so the mixed material does not start to cure before it reaches the cavity.
Mold temperature and cure. LSR is injected into a hot mold, commonly about 180–200°C / 356–392°F, where it cures; thin parts cure quickly. HCR is compression or transfer molded at a temperature set by its cure system, or extruded and cured continuously, typically in a hot-air line.
Shrinkage and post-cure. LSR typically shrinks about 2.5–3% as it cools from the hot mold, and post-cure can add roughly another 0.5%. Many parts, especially peroxide-cured HCR and food or medical parts, are post-cured in a vented oven, commonly about 4 hours at about 200°C / 392°F, to drive off volatiles and lower compression set. Follow the data sheet schedule.
Scrap. Cured silicone cannot be remelted or reground back into the process, so sprues, flash and rejects are lost material. LSR cold-runner tools keep runner waste low. Clean, uncured HCR trim can often go back on the mill while it is within its shelf life.
Most common defects. Flash: LSR can flash in gaps as small as about 0.005 mm / 0.0002 in, so tools need tight shutoffs and carefully placed vents, often with vacuum, and flash grows as tools wear. See flash. Cure inhibition: platinum-cured grades can stay tacky or uncured where they touch sulfur (from latex gloves or sulfur-cured rubber), tin compounds (from condensation-cure silicones), amines and some other chemicals. Keep them away from the material and the tool.

What to put on the purchase order

Type and cure system: two-part liquid (LSR) with its mix ratio, or gum (HCR), catalyzed or not, and platinum or peroxide cure. They do not interchange on the same equipment.
Hardness: Shore A (or Shore OO for gels) with a tolerance, and whether it is measured before or after post-cure.
Properties the part depends on: tear strength by the test method you use now, compression set at your temperature and time, and resistance to any fluids, oils or steam the part sees.
Color: natural, translucent or a match. LSR is often colored at the press with a pigment paste, so say whether the material should come colored.
Documents by grade: the producer’s FDA letter, ISO 10993 or USP Class VI reports, and UL recognition, which is grade-specific and color-specific. Note any post-cure the documents assume.
Packaging and dating: pail or drum size that fits your pump or mill, whether A and B sides must come from matched lots for your grade, and the shelf life remaining when the material arrives.
COA values to check: hardness, specific gravity, tensile strength and elongation, tear strength, and viscosity (LSR) or plasticity (HCR) if the grade lists them.

When to consider something else

If the part stays below about 125°C / 257°F and you want lower material cost, better tear resistance and reusable scrap, look at TPV, and see TPV vs. silicone and TPV vs. other elastomers.
If you need a soft-touch grip overmolded onto PP, ABS or PC with thermoplastic cycle times, look at TPE / TPV.
If abrasion, cutting or oil is the main failure, look at TPU.
If you need rigid housings, labware or packaging with food or medical documentation, see FDA and medical-grade resins.
If the part is rigid or a tube or lining that sees aggressive chemicals at high heat, look at fluoropolymers.

Common questions

What is the difference between LSR and HCR?

LSR (liquid silicone rubber) is a pourable two-part liquid that is pumped, mixed and injection molded into a hot mold, which suits automated, high-volume parts. HCR (high-consistency rubber) is a stiff gum mixed with its cure system on a mill, then compression molded, transfer molded or extruded. The choice usually follows your process and equipment.

Is silicone rubber food safe?

Food-contact compliance belongs to the exact grade, not the family. In the U.S., producers usually document food-contact silicone against FDA 21 CFR 177.2600, often with a post-cure requirement. Ask for the producer’s FDA letter for the exact grade and follow the post-cure it calls for.

What temperature can silicone rubber handle?

Typical grades work from about −55 to 200°C / −67 to 392°F, and some heat-stabilized grades are rated higher. Fluorosilicone resists fuels and oils better but usually has a lower top-end rating.

Why is my silicone not curing?

With platinum-cured grades, the usual cause is cure inhibition: contact with sulfur, tin compounds, amines or some other chemicals stops the cure where they touch. Other causes are a wrong mix ratio, material past its shelf life, or a mold that is too cool. Check the meter ratio and dates, clean the tool, and run a test shot.

TPV vs. silicone TPV vs. other elastomers TPE / TPV TPU FDA & medical-grade resins Seals taking a set

Silicone rubber supplier: grades for molding and extrusion