| Property | Value |
|---|---|
| Temperature range | -55 °C to +200 °C |
| Hardness | 10–70 Shore A, softer than most families reach |
| Biocompatibility | USP Class VI and ISO 10993 grades available |
| Contains fluorine | No, unless a fluorosilicone grade is specified |
The widest temperature range you can buy without fluorine
Silicone's siloxane backbone is inorganic, and it gives the family a service range that runs from deep cold to sustained heat with very little change in properties across it. A silicone seal that is flexible at -50 °C is the same seal that holds shape at 200 °C. Very few materials do both ends, and for parts that cycle across a wide range rather than sitting at one temperature, that stability is the reason to choose it.
Biocompatibility, and what the grades actually mean
USP Class VI and ISO 10993 are biological-reactivity test protocols with defined test batteries behind them. A grade certified to them has been through the testing, which is why LSR is the default for anything with patient contact: medical device seals and overmolded grips, tubing components, respiratory and drug-delivery parts. The same cleanliness is why it dominates food-contact and infant products.
It is worth being precise about what the certificate covers. The raw material grade is certified, and the finished part still has to be molded, handled, and documented in a way that preserves that, which is a process question rather than a material one.
Where LSR is the wrong choice
Mechanical strength is the real limit. Silicone has low tensile and tear strength compared with nitrile or polyurethane, so a part that takes abrasion, sharp installation, or repeated high-strain flexing will not last, however good its temperature range looks. It also swells in fuels and petroleum oils, which rules out most oil-wetted sealing.
The other consideration is commercial. LSR needs precision tooling and an injection system built for it, so the tooling investment is higher than a compression-molded equivalent. That cost amortizes well at volume and badly at low volume, which is why prototype quantities are sometimes better served by a compression-molded silicone even when the production part will be LSR.
Typical uses
- Medical device components and overmolded grips
- Micro and precision parts with features too fine for compression molding
- Two-shot and overmolded assemblies onto plastic or metal substrates
- Food-contact, infant, and consumer products
- Seals and gaskets that cycle across a wide temperature range