Liquid silicone rubber is a two-part, platinum-cured silicone supplied as a flowable liquid rather than a gum. It cures fast in a heated mold, releases cleanly, and holds tolerances that solid silicone struggles to match. That combination explains why it has moved from niche medical parts into automotive, electronics, and consumer products.
Liquid Silicone Rubber Properties That Matter in Design
LSR offers high clarity, good tear strength, strong rebound, and resistance to yellowing. It stays flexible from roughly -50 to 200 degrees Celsius depending on grade, resists water and many chemicals, and can be formulated for electrical conductivity or thermal conduction. Shrinkage is low, around 0.1 to 0.3 percent, which suits precision parts.
How LSR Differs From HTV Silicone
High-temperature vulcanized silicone is a gum that must be mixed, cut, and formed under high pressure. LSR arrives pre-mixed in two components, is metered by a dosing pump, and cures in seconds because platinum catalysis is fast. The result is tighter dimensional control, less manual handling, and lower contamination risk, at the cost of specialized equipment.
Medical Applications
Biocompatibility, sterilization resistance, and transparency make LSR a natural fit for seals, valves, catheters, and wearable device interfaces. Medical grades are supported by ISO 10993 testing and can be processed in an ISO 13485 environment. Soft grades feel comfortable against skin, which matters for long-wear devices.
Automotive and Electronics Uses
Under-bonnet components benefit from heat and oil resistance. Connector seals, battery thermal pads, sensor gaskets, and keypads use LSR for reliable sealing across temperature swings. Flame-retardant grades serve enclosures, and optically clear grades serve light guides and lenses.
Consumer and Industrial Parts
Watch bands, cookware gaskets, and grips use LSR where skin contact and heat resistance matter. Industrial uses include diaphragm valves and food-grade seals, where the material must resist cleaning chemicals without hardening.
Why Injection Molding Suits LSR
- Cold runner systems keep mixed material from curing in the runner
- Short cure times support high cavitation and fast cycles
- Automated metering gives consistent shot weight
- Low shrinkage holds tight tolerances on small parts
- Clean demolding suits high-clarity and medical parts
Processing Considerations
Mold temperature typically runs 150 to 200 degrees Celsius, and cure time depends on wall thickness. Vents must be fine enough to release air but tight enough to prevent flash, because LSR flows into gaps of a few micrometers. Pigment changes require purging, and post-curing may be needed for parts that will contact food or body tissue.
Frequently Asked Questions
Is LSR the same as silicone rubber?
It is one form of silicone. LSR is the liquid, platinum-cured type; HTV is the solid gum type.
Can LSR be overmolded onto plastic?
Yes, and the bond is strong on compatible substrates such as PA, PBT, and PPS.
Why is LSR more expensive per kilogram?
Material cost is higher, but faster cycles, lower scrap, and less manual handling often reduce total part cost.
Conclusion
Liquid silicone rubber is chosen for clarity, heat resistance, and dimensional stability, and it performs best in a properly equipped injection process. For related reading, see liquid silicone rubber reference, our LSR double injection molding guide, and medical silicone molding guide. Contact TCHD to review your application.