Silicone Injection Molding

LSR vs. HCR: Choosing the Right Silicone

Silicone rubber comes in two processing families. LSR is a two-component liquid that is metered, mixed and injected directly into a heated mold, where it vulcanizes in seconds to minutes. It suits high-volume, thin-wall parts — seals, gaskets, diaphragms, valves, baby-care and medical components — and holds tight tolerances with excellent batch repeatability. HCR (high-consistency rubber) is supplied as solid gum, is processed more like a traditional rubber, and is the better choice for larger parts, thick sections and applications that need maximum tear strength.

Both families share the properties buyers actually spec: service temperature from roughly −50 °C to 200 °C, chemical and weathering resistance, low compression set and biocompatibility in validated grades. We run silicone on dedicated molding capacity with controlled cure temperature and cycle parameters, so durometer and dimensions stay stable across the run. For the process end-to-end, see our dedicated LSR injection molding service page.

Medical & Consumer Applications

• Medical: syringe components, respiratory seals, surgical device grips, catheter accessories and implant-adjacent parts — processed under ISO 13485 control with ISO 10993-validated materials on request.
• Consumer: baby bottle nipples, food-grade seals, wearable straps and soft-touch overmolded grips.
• Industrial & automotive: gaskets, O-rings, dust seals and connector seals that must survive heat, oil and weather.
• Multi-material: silicone overmolded onto PC, PBT, nylon or metal inserts — often with insert positioning held to ±0.02 mm on our vertical presses.

Because silicone molds are typically machined aluminum or steel with cold-runner or injection-compression design, DFM matters more than with thermoplastics — flash control, venting and cure-time estimation decide cycle cost. Our engineers review the part before tooling and we build the mold in-house. For medical-grade programs, documentation — material certs, batch traceability and inspection reports — is standard, and you can see the systems behind it on the certifications page.

Design & Process Notes

Three things separate a good silicone program from a painful one. First, wall thickness: silicone cures from the outside in, so thick sections extend cycle time sharply — design for 0.5–3 mm where possible. Second, flash control: LSR is thin and finds every gap, so mold fit and venting are designed in, not fixed in production. Third, cure temperature and shot size must be tuned together; we record parameters per batch so repeat orders reproduce the first article.

For market context, First Mold lists silicone among its 100+ supported materials and advertises ±0.01 mm molding tolerance for engineering thermoplastics (firstmold.com) — a useful benchmark when comparing quotes. Our own process notes and tolerances are part of the DFM report you receive before any tooling commitment.