Can you injection mold soft tpu ?

Yes, TPU (Thermoplastic Polyurethane) can be injection molded, including softer grades. Here's what you need to know:

Hardness Range Soft TPU typically refers to Shore A 60–85, though TPU spans from about Shore A 60 all the way to Shore D 80. The softer grades are absolutely moldable but require more care.

Key Processing Considerations

Temperature: Melt temperatures generally run 190–220°C depending on the grade. Softer grades tend to need lower temperatures.

Drying: TPU is highly hygroscopic — it must be dried thoroughly before molding (typically 2–4 hours at 80–100°C) or you'll get hydrolytic degradation, splay, and poor surface finish.

Injection speed & pressure: Soft TPU flows well but is shear-sensitive. Use moderate injection speeds and avoid excessive back pressure to prevent material degradation.

Mold design:

• Use generous draft angles (2–5°) since soft parts can deform during ejection

• Avoid sharp undercuts — soft TPU can flex out of mild undercuts, which is actually an advantage

• Ejector pins need to be well-distributed to avoid tearing soft parts

• Venting is important to prevent burn marks

Shrinkage: Soft TPU has higher shrinkage (typically 1.5–2.5%) than rigid materials, so tooling dimensions need to account for this.

Grades to Look At Suppliers like BASF (Elastollan), Lubrizol (Estane), Covestro (Desmopan), and Huntsman offer injection-moldable soft TPU grades specifically formulated for this process.

Common Applications Soft-touch grips, phone cases, seals, medical device components, footwear parts, and cable overmolds.

Challenges to Watch

• Sticking in the mold (mold release agents or coatings help)

• Stringing during gate separation

• Long cycle times due to soft parts needing more cooling before ejection

Overall it's a well-established process — just requires dialing in your drying, temperatures, and ejection strategy more carefully than with rigid thermoplastics.