TPU, commodity TPE compounds and TPC elastomers solve different flexible-part problems. Select the exact grade from the required deformation, temperature, fluid exposure, abrasion, fatigue and bonding duty; Shore hardness alone cannot make the decision.
This guide is a material-family screening tool for molded flexible parts. It does not replace grade-specific supplier data or an overmold bond trial. For interface and tooling decisions, use CKMOLD’s insert molding and overmolding service and validate the exact hard-soft pair.
Start With Elastic Duty, Not Shore Hardness
Define compression, tension, bending, sealing pressure, strain range, cycle count and acceptable permanent set. Two materials with the same Shore A value can have very different modulus curves, tear strength and recovery. Review stress-relaxation or compression-set data at the actual temperature and aging time, then test the molded geometry rather than relying on a single hardness reading.
Use TPU for Toughness and Abrasion When Chemistry Fits
TPU grades are widely used for wheels, cable features, wear surfaces and protective overmolds because they can combine tensile strength, abrasion resistance and toughness. Polyester- and polyether-based TPUs differ in hydrolysis, microbial and oil behavior. Moisture control is important during processing, and some grades can yellow or lose properties under UV or prolonged heat without the right stabilization.
Use Commodity TPEs for Soft Touch and Efficient Overmolding
Styrenic TPEs and thermoplastic vulcanizates can offer broad hardness ranges, easy coloring and relatively forgiving processing for grips, seals and flexible features. Their oil resistance, heat capability, compression set and abrasion vary significantly. Adhesion to PP, ABS, PC or nylon is compound-specific; mechanical interlocks remain useful when chemical bonding or surface cleanliness cannot be supported.
Use TPC When Heat and Dynamic Flexing Drive the Design
Thermoplastic copolyester elastomers can provide strong fatigue behavior, toughness and performance at temperatures where some softer TPEs lose load. They may suit bellows, ducts, clips and dynamic components. Hydrolysis, chemical exposure, required softness, drying and higher material cost must be checked. TPC is not automatically the best seal material when low compression set at one condition is the dominant need.
Validate Overmolding as an Interface System
Substrate grade, surface age, contamination, insert temperature, flow direction, pressure and cooling affect bond strength. Use peel, tensile or torque tests that represent the feature and environment. Molded-in stress, undercuts and shutoff design can influence failure more than nominal adhesion. Define whether failure should occur cohesively in the elastomer, at the interface or through a mechanical lock.
TPU vs TPE vs TPC: Design and Validation Checklist
- Define strain mode, cycle life, temperature and allowable permanent set.
- Compare exact compounds at the required hardness, color and thickness.
- Test oils, cleaners, humidity, UV, abrasion and heat aging as relevant.
- Review drying, shear, gate, venting, ejection and runner economics.
- Validate substrate adhesion and mechanical locks on production-like parts.
Frequently Asked Questions
Is TPU a TPE?
Yes. TPU is a thermoplastic polyurethane and belongs to the broader thermoplastic-elastomer family.
Which elastomer bonds best to ABS?
Bonding is grade-specific. Use a compound designed for the substrate, control surface and process conditions, and validate the actual interface.
Can hardness predict compression set?
No. Hardness measures indentation response; long-term recovery depends on polymer structure, temperature, strain and time.
Primary reference points
- Lubrizol: TPU Injection Molding Processing Guide (supplier guidance for its TPU products)
- Celanese: Hytrel thermoplastic polyester elastomers (supplier overview for the TPC family)
Next step
Send the rigid substrate grade, candidate elastomer grades, target hardness, wall section, service temperature, chemicals, loading mode and annual volume for a project-specific molding review. The result should be an approved material pair and validation plan, not a family-level promise.