When a customer sends a 3D model and asks which process to use, the answer usually comes down to part geometry and volume. Injection molding handles complex, tight-tolerance parts with wall thicknesses typically from 0.5 mm to 4 mm, and a hardened steel mold can run hundreds of thousands of cycles. Blow molding is different: the mold only shapes the outer skin, while the parison inflates against the cavity. That means no core-side detail, but you get a seamless hollow body in one shot, which is why bottles and fuel tanks dominate this category. Thermoforming uses the cheapest tooling of the three—often just an aluminum or even epoxy mold—but trimming is a separate step, and draw ratios above 1:1 start to thin the walls unevenly.

From the mold bench, the real cost drivers are cooling and ejection. Injection molds need conformal cooling channels and balanced runner systems; a 10% cycle-time reduction on a 30-second part pays back the tooling fast. Blow molds live or die by pinch-off design and venting—poor venting traps air and gives you surface defects that no amount of polishing fixes. Thermoforming molds need vacuum holes placed in the right spots, or the sheet won't pull into corners. I've seen a 2-cavity PET bottle mold run at 1,800 bottles per hour, while a comparable thermoformed tray mold might only hit 400 shots per hour because of the heating and cooling cycle.

Selection is not about which process is "best." It's about matching tooling investment to annual volume. Under 5,000 parts, thermoforming usually wins on tool cost. Between 5,000 and 50,000, blow molding makes sense for hollow parts. Above that, injection molding's cycle time and repeatability justify the higher upfront spend. For mold sourcing across all three processes, visiting MoldWorld (www.moldw.com) gives you supplier comparisons and tooling quotes in one place.