A Beginner's Guide to Liquid Silicone Rubber (LSR)

What is Liquid Silicone Rubber?

LSR is a two-part, platinum-cured elastomer supplied as a liquid. Unlike solid silicone rubber, LSR is injected into molds in liquid form, where it cures rapidly under heat to form flexible, durable silicone parts.

Key Characteristics

Heat resistant (typically -40°C to 230°C)

Chemically inert and biocompatible

Excellent elasticity and tear resistance

Transparent/translucent options available

FDA compliant grades for medical/food applications

Common Applications

Medical: seals, gaskets, valves, baby bottle nipples

Automotive: seals, gaskets, vibration dampeners

Consumer: kitchenware, wearable tech, baby products

Industrial: seals, electrical insulation, membranes

Manufacturing Process (Liquid Injection Molding)

Mixing: Two components (base + catalyst) are precisely metered and mixed

Injection: Liquid is injected into a heated mold

Curing: Heat causes rapid cross-linking (typically 15-90 seconds)

Demolding: Finished parts are removed (no post-cure usually needed)

Advantages Over Other Materials

Fast cycle times (seconds vs. minutes for solid silicone)

High precision with complex geometries

Excellent part consistency

Automated production with minimal waste

No by-products during curing

Design Considerations for Beginners

Draft angles: 1-2° recommended for easy demolding

Wall thickness: Keep uniform (typically 0.5-5mm)

Undercuts: Generally avoided unless using complex tooling

Gating: Location affects flow and part quality

Shrinkage: Typically 2-4% - must be accounted for in mold design

Getting Started Tips

Start simple: Begin with basic shapes before complex designs

Prototype: Use 3D printing to test designs before tooling

Partner with experts: Work with experienced molders initially

Material selection: Choose food/medical grade if needed

Tooling awareness: Steel molds are expensive but durable for LSR

Common Mistakes to Avoid

Ignoring material flow characteristics in design

Inadequate venting in molds causing trapped air

Incorrect mixing ratios

Insufficient mold temperature control

Designing parts that are difficult to demold

LSR offers unique advantages for precision rubber parts, but requires understanding its specific processing requirements to achieve optimal results.