How To Select The Silicone Rubber Row Material | Types Summary
Choosing a silicone rubber material by category name is how projects end up with a part that meets the drawing and fails in service. The name on the datasheet describes a family; the application decides which property inside that family matters.
This article compares the grades that appear most often in custom moulding and sets out the four application questions that narrow the choice before a compound is named.
What Silicone Rubber Material Has to Match
Four questions narrow the choice faster than any datasheet. What does the part touch: skin, food, fuel, solvent, nothing? What temperature range does it see, including cleaning and sterilisation? How much movement or compression does it carry, and for how long? Does it have to conduct electricity?
Answer those and most grades eliminate themselves. A part that touches food cannot use a general-purpose compound regardless of how well it performs mechanically. A part that sits in oil needs a grade formulated for it, because standard silicone swells.
Silicone Rubber Material Types Compared
| Grade | Typical use | Limit to watch |
|---|---|---|
| General purpose | Gaskets, keys, covers, industrial parts | Not for food, medical or oil contact |
| Food contact | Seals, kitchen parts, dispensing components | Confirm the compliance route for the market |
| Medical grade | Device covers, tubing, instrument parts | Requires a validated, traceable supply |
| Liquid silicone (LSR) | Small precise parts, high volume | Needs metering equipment and a clean environment |
| High tear | Thin webs, keypads, parts demoulded hot | Harder to pigment consistently in some colours |
| High temperature | Parts near heat sources, ovens, engines | Check retention of elasticity, not only survival |
| Conductive | Keypad pills, grounding contacts | Resistance drifts with age and contamination |
| Oil resistant | Automotive and machinery seals | Not identical to fluorosilicone performance |
Choosing silicone rubber material for keypads and seals
A keypad wants a high-tear grade at 50 to 70 Shore A, because thin webs fail in tension during demoulding and assembly. A static seal wants a low-compression-set grade at 30 to 50 Shore A, because it must keep pushing back after years under load. Those two requirements point at different compounds even when the parts look similar, which is why the same supplier may recommend different grades for two parts from the same drawing family.
Hardness, Colour and Grade Within One Silicone Rubber Material
Hardness is set by filler loading, so a change of hardness is a change of compound and usually a small change of shrinkage. That matters for tools with tight dimensions. Colour is a pigment addition, and pale or translucent colours are harder to hold consistently than black or dark colours.
Food contact and medical grades are families rather than single compounds, and the compliance route depends on the market the product is sold into. Ask what documentation the supplier can provide and keep it with the part record, because a later change of compound can invalidate it.
Cost follows the grade rather than the hardness. A high-tear or medical grade can cost materially more per kilogram than a general-purpose compound, and that difference belongs in the quotation rather than in a later change order.
How to Document a Silicone Rubber Material Choice
Put four lines on the drawing: compound family, hardness with a tolerance band, colour reference, and the compliance requirement. Add the property that matters most for the application, whether that is tear resistance, compression set or conductivity, and say how it will be verified.
Then agree what would trigger a re-qualification. A change of compound supplier, a change of hardness, or a change of colour all affect the part, and a supplier who notifies those changes is worth more than one who quotes lower.
Where the part combines silicone with another material, the material choice interacts with the process. Our notes on over-moulding explain how substrate and overmould have to be selected together.
A short silicone rubber material checklist
- Contact surface: skin, food, chemical, or none.
- Temperature range including cleaning and sterilisation cycles.
- Static or dynamic load, and the compression it carries.
- Electrical requirement, if any, and the resistance window.
- Property to verify at first article, beyond dimensions and hardness.
Is food-grade silicone the same as medical-grade silicone?
No. Both are formulated for contact, but the compliance routes, documentation and typical validation differ. A grade accepted for food contact is not automatically accepted for a medical device, and the reverse is also true.
Can a general-purpose compound be used outdoors?
Usually yes for UV and weather exposure, because silicone resists both. The constraint is more often colour stability and the presence of oils or solvents than sunlight itself.
Pick the silicone rubber material from the contact surface, the temperature range, the load and the electrical requirement, then choose the grade that carries the property you will actually verify. Name the compound family, the hardness band, the colour and the compliance route on the drawing, and agree what change would force a re-qualification.
