Liquid Silicone Rubber (LSR) molding injects a two-part platinum-cured silicone through a cold runner into a hot mold — the mirror image of thermoplastic injection.
Where LSR wins: very tight tolerances (±0.05 mm on small features), essentially flash-free parting lines, complex geometries with undercuts and thin walls, full automation with pico-scale shot control, and platinum chemistry that leaves no peroxide by-products — the reason medical and baby-care parts default to LSR.
Where compression molding (HCR) still wins: unit cost for medium-large parts, tooling cost for simple geometries, low-to-mid volumes, and compounds with high mechanical fillers.
Practical selection: annual volume above ~50k pieces with tight tolerance or cleanliness requirements usually justifies LSR tooling; prototypes and 1k-20k batches are typically more economical in compression molding. Many programs start in compression molding for sampling, then transfer to LSR for mass production — the part design should be reviewed for LSR rules (uniform wall, generous radii, draft) before tooling kickoff.