LSR Injection vs Compression Molding: Which Process Fits Your Part?

One of the first questions we ask new customers is not "what material do you want" but "what does your part need to do, and how many do you need". Because in silicone manufacturing, the process choice — liquid injection molding (LIM) or compression molding — is usually decided by volume, tolerance and cosmetic requirements, not by preference.

Tooling and unit cost

LSR injection molds cost more upfront: cold-runner systems, tight shut-off surfaces and precision heating zones push tooling 30–80% above a comparable compression mold. In exchange, LIM delivers cycle times of 30–90 seconds with zero manual loading, so unit cost drops sharply with volume. Compression molding has cheaper tooling and suits lower volumes, but flash removal adds labor that never scales well.

Precision and cleanliness

For medical, optical or baby-care parts, LSR wins decisively: flash-free parting lines, tolerances down to ±0.05 mm on small features, and a closed system that keeps the class-100,000 cleanroom environment from touching uncured material. Compression-molded parts typically need deflashing, washing and inspection steps that add cost and contamination risk.

• Choose LSR injection when: volume > 10k/year, tolerances < ±0.1 mm, medical/food contact, overmolding in one shot
• Choose compression when: volume < 10k/year, large simple cross-sections, specialty compounds (fluorosilicone, conductive) that are hard to pump

The hybrid reality

We run both processes under one roof precisely because real products are mixed: a medical pump may need an LSR diaphragm, a compression-molded grommet and an overmolded metal insert. If your supplier only runs one process, expect their quote to quietly push your design toward their equipment. Ask for the process trade-off in writing.