LSR vs Solid Silicone

LSR vs Solid Silicone: Process and Economics Comparison

"Solid silicone" (HTV/HCR) and LSR are the two main processing forms of silicone rubber. While both use the same Si–O polymer backbone and can achieve similar final properties, their processing technologies, tooling requirements, production economics, and design capabilities are fundamentally different. This guide helps engineers and procurement teams determine which form to specify.

Processing Technology Comparison

Solid silicone (HTV) processing:

1. Compound supplied as pre-mixed slab or strip (putty-like consistency)
2. Weighed and cut to shot weight manually or by machine
3. Placed in lower mold half
4. Press closes, compound flows under pressure into cavity
5. Cured at 150–180 °C for 3–10 minutes
6. Part removed, excess flash trimmed manually or by cryogenic deflashing
7. Post-cure in oven (200 °C, 4 hours) for peroxide-cured grades

LSR (Liquid Silicone Rubber) processing:

1. Part A (polymer + catalyst) and Part B (crosslinker + inhibitor) pumped from drums at 1:1 ratio
2. Mixed in static mixer, temperature controlled at 5–15 °C to prevent premature cure
3. Injected through cold runner into heated mold (150–200 °C)
4. Cures in 30–90 seconds (addition cure, no post-cure required)
5. Part ejected automatically, flash-free

Tooling and Capital Cost

HTV tooling: Simple compression molds in P20 or H13 tool steel. No cold runner, no injection system. Single-cavity tool for prototyping costs $2,000–$8,000; multi-cavity production tools $10,000–$50,000 depending on cavity count and complexity.

LSR tooling: High-precision injection tools with cold runner manifold, hydraulic injection, and temperature-controlled mold halves. Prototype tool: $15,000–$40,000; production multi-cavity tool: $50,000–$200,000+.

The LSR tooling cost disadvantage is overcome at high volumes by lower cycle time, labor savings, and flash elimination.

Part Geometry Capability

For parts requiring thin walls, undercuts, or direct overmolding onto engineering plastics, LSR injection is the only viable option.

Production Volume Economics

Breakeven analysis (approximate, application-dependent):

At volumes below approximately 30,000–50,000 pieces/year, HTV compression molding has lower total cost because the tooling investment is recovered over fewer cycles. Above 50,000–100,000 pieces/year, LSR's faster cycle time, multi-cavity capability (16–64 cavities), and labor-free operation typically result in lower per-piece cost despite the higher tooling investment.

For comparison: a 16-cavity HTV compression tool running 5-minute cycles produces 192 pieces/hour; a 16-cavity LSR injection tool running 60-second cycles produces 960 pieces/hour — 5× the output.

Certifications: Comparable at the Same Tier

Both HTV and LSR are available in FDA 21 CFR, LFGB, USP Class VI, and RoHS-compliant grades. Neither form has an inherent certification advantage over the other, as both can use platinum addition cure. LSR medical grades are slightly easier to qualify for clean-room production due to the enclosed LIM process.

Decision Summary

Choose solid silicone (HTV) when: volume is low (<50K/year), extrusion is required, Shore hardness >70A, or simple geometry at minimum tooling cost is needed.

Choose LSR when: volume is high (>100K/year), geometry requires undercuts or thin walls (<1 mm), overmolding onto plastic is needed, flash-free production is required, or clean-room enclosed production is mandated.

Contact us to discuss your application and connect with qualified solid silicone and LSR processing partners.