Thermosets. Silicones. Large structural.

Injection molding: thermoplastic melts in barrel, injects into cold mold, cools and solidifies. Cycle 20-90 seconds. Compression molding: material placed in heated mold, pressed, cures via heat + time. Cycle 2-15 minutes. Injection is faster, lower cost for high volume, limited to thermoplastics. Compression handles thermosets, has lower tooling cost, allows larger parts, lower volume economics.

Thermosets offer: higher heat resistance (phenolic: continuous 150°C; thermoplastics: 80-130°C typical). Better chemical resistance for some chemistries. Higher stiffness at elevated temperature. Better electrical insulation. Cannot be remelted (once cured, stays cured). For heat-critical, structural, or electrical applications where thermoplastics reach their limits, thermosets extend capability.

Compression mold tooling: $5,000-20,000 for typical parts. Injection mold tooling: $15,000-80,000. Compression tooling simpler (no runners, no gates, less complex design). Lower tooling cost makes compression economical at lower volumes — below 1,000 pieces annually. For higher volume, injection molding amortizes faster.

Compression molding handles larger parts than injection: up to 2m × 2m practical maximum. Injection molding limited by press size and clamp tonnage — typically < 1m in any dimension without massive machines. For large parts (automotive body panels, bathroom fixtures, industrial covers), compression molding enables sizes impossible for injection.

Compression molding sweet spot: 500-10,000 parts annually. Below 500: CNC or casting often cheaper. Above 10,000: injection molding typically better (faster cycle, lower per-part cost). For complex thermoset parts, compression remains optimal across all production volumes because thermosets cannot be injection molded.

Compression mold tooling: 6-10 weeks. First article production: 1-2 weeks after tool. Production delivery: 2-4 weeks per order. Compression molding cycle times are slower than injection — 2-15 minute cure times mean lower per-day output. Plan longer lead times for compression programs vs injection programs.