Heat stability
Holds flexibility across a wider temperature range than most TPEs.
Liquid silicone rubber
Liquid Silicone Rubber (LSR): Seals, Gaskets, and How to Quote
LSR for seals and gaskets, compared with TPE when heat is the driver. LSR molding and LSR overmolding are in scope when named on the RFQ.
Liquid silicone rubber
What Liquid silicone rubber is and when it is used
Properties, routing vs TPE, and how to quote LSR when the RFQ scopes it.
Liquid silicone rubber (LSR) is a two-part thermoset silicone that is injected into a heated mold and cured, rather than melted and cooled like a thermoplastic. It holds its properties across a wide temperature range, resists aging and ozone, and is chosen for seals, gaskets, soft keypads, and parts that see repeated heat or sterilization. LSR uses its own tooling, metering, and cure process, so it sits on a different supply chain from thermoplastic injection molding. NetProto focuses on thermoplastic molding and overmolding. This page explains LSR so you can compare it with TPE, TPU, and flexible PVC, which are often the faster and lower cost path when the service temperature allows. For fuel-system seals where fuel and oil resistance is the concern, see Fluorosilicone .
Key traits
Why engineers specify Liquid silicone rubber
Material characteristics for comparison. No processing parameters on this page.
Aging
Strong resistance to ozone, UV, and long-term compression.
Process
Thermoset cure in a heated mold, not melt and cool.
Alternatives
TPE, TPU, and TPV cover many soft parts when heat allows.
Routing
Liquid silicone rubber or a thermoplastic alternative
Pick the material family by the requirement that matters most.
| Requirement | Start with | Why |
|---|---|---|
| Sustained high heat or repeated sterilization | LSR | Thermoset stability across temperature |
| Soft-touch overmold on PP, ABS, or PC | TPE | Bonds in a thermoplastic overmold |
| Abrasion and tear resistance | TPU | Tougher wear surface |
| Seals with compression set at moderate heat | TPV | Thermoplastic seal option |
Selection
Selection checklist
Use these points to decide between silicone and a thermoplastic elastomer.
Hardness range (Shore A) the part needs
Service temperature range, including peaks
Regulatory documentation your program requires (from the silicone supplier)
Color options and translucency
Post-cure requirement for low volatile content
Whether a thermoplastic elastomer could meet the same requirement
Compare and explore
Related materials
Thermoplastic alternatives and sibling pages.
TPE family hub
Thermoplastic elastomer routing.
Learn more
TPU
Abrasion-resistant elastomer.
Learn more
TPV
Thermoplastic vulcanizate for soft seals and grips.
Learn more
Flexible PVC
Plasticized vinyl for soft parts.
Learn more
Overmolding
Rigid plus soft thermoplastic programs.
Learn more
Reading a material datasheet
What the TDS values mean for a molded part.
Reading a material datasheetQuote guides
Quote LSR and the nearby decisions
Process page, overmold RFQ, and when TPE is the first quote.
How LSR molding runs
Cold mix, hot cure, and what the RFQ should name.
How LSR molding runsOvermolding services
When the silicone is a skin on a rigid part.
Overmolding servicesLSR vs TPE overmolding
Which soft skin to quote first.
LSR vs TPE overmoldingLSR overmold design guide
Substrate, flash, and what to settle before steel.
LSR overmold design guideQuote overmolding or two-shot
Two bodies, resin families, and named bond faces.
Quote overmolding or two-shotInstant quote platform
Upload CAD. Name LSR or LSR overmold on the RFQ.
Instant quote platformFAQ
Liquid silicone rubber FAQ
What is the core difference between LSR and TPE?
LSR is a thermoset silicone that keeps properties at higher heat and resists aging. TPE is a thermoplastic that melts and freezes in a standard press. Name the family on the RFQ. If a thermoplastic skin is enough, start with TPE.
Does NetProto mold LSR parts?
Yes. Liquid silicone rubber (LSR) molding and LSR overmolding are in scope when the program is named on the RFQ, the same pattern as other molding services. Upload CAD and mark silicone-only or overmolded.
When is TPE a good substitute for LSR?
When service temperature is moderate and the part needs soft touch, grip, or a simple seal, TPE or TPV often meets the requirement. At NetProto, we suggest comparing compression set and heat requirements on the TPE and TPV pages.
Why does LSR need post-cure?
Post-cure drives off volatile residues for some programs. The requirement comes from your spec and the silicone supplier. NetProto does not publish post-cure times or temperatures as a catalog spec.
Is LSR used for regulated applications?
Some silicone grades are offered for regulated uses, and the supporting documentation comes from the silicone supplier. NetProto does not make regulatory claims for LSR parts and recommends confirming requirements with your compliance team.
How does LSR tooling differ from thermoplastic tooling?
LSR molds are heated so the mix can cure. Thermoplastic molds are cooled so the melt can freeze. Both are steel tools. Name LSR on the RFQ so the quote does not assume a thermoplastic cell.
Next step
Ready to quote an LSR part?
Upload CAD. Name LSR or LSR overmold on the RFQ. Tooling and piece price come back with DFM notes.