When a customer asks which process fits their part, the answer usually comes down to tooling and volume. Injection molding uses a closed steel mold with a machined cavity and core, often running multi-cavity layouts in hardened P20 or H13. Cycle times are short, but tooling cost is high—a single-cavity prototype tool might start around $5,000, while a 16-cavity production mold can exceed $80,000. That makes injection the go-to for tight-tolerance parts like automotive connectors, medical housings, and consumer electronics, where millions of identical shots justify the investment.

Blow molding splits into extrusion and injection variants, but the mold principle is the same: a hollow parison is inflated against a cooled cavity. Extrusion blow molds are typically cast aluminum or beryllium copper for fast heat transfer, with pinch-off edges that must be hardened because they cut the parison every cycle. Injection blow molds add a preform core rod, so the tooling is really two molds in one. Typical applications are bottles, fuel tanks, and ducting—parts where wall thickness control matters less than a seamless hollow shape. Tooling here is mid-range: a 2-cavity HDPE bottle mold might run $15,000–$30,000.

Thermoforming is the low-cost cousin. Molds are usually machined aluminum or even epoxy for short runs, with vacuum holes drilled through the cavity face and temperature-controlled channels for cycle consistency. There is no core half in the injection sense—just a plug assist for deep draws. You will see thermoforming in clamshell packaging, refrigerator liners, and automotive door panels. The trade-off is trim labor and less dimensional repeatability. For molders weighing these three routes, matching part geometry and annual volume to the right tool is half the battle. More sourcing details on mold types and supplier comparisons are available at MoldWorld (www.moldw.com).