Choose TPU when thermoplastic processing, abrasion/tear performance and integrated molding suit the part; choose a thermoset rubber when its heat, chemical, compression or elastic behavior better matches the service. Neither family is universally more flexible, durable or economical. Compare exact compounds under the same requirements.
Clarify what “rubber” means
Rubber may refer to EPDM, silicone, nitrile (NBR), natural rubber, FKM or another crosslinked elastomer. These compounds differ greatly. TPU is also a family, with polyester-, polyether- and other grade variations. A useful comparison therefore names the specific rubber compound and TPU grade rather than comparing two generic labels.
Engineering comparison
| Decision factor | TPU | Thermoset rubber |
|---|---|---|
| Processing | Injection moldable and remeltable; drying/process control can be critical | Compression, transfer or injection molding with vulcanization/cure |
| Wear and tear | Many grades offer strong abrasion and tear performance | Varies widely by rubber family and formulation |
| Compression/sealing | Suitable grades can seal, but creep and compression set require validation | Many rubber compounds are optimized for long-term sealing |
| Heat and chemicals | Grade-specific; hydrolysis or swelling can limit some applications | EPDM, silicone, NBR, FKM and others cover different exposure ranges |
| Color and surface | Broad colorability; appearance depends on grade and process | Broad formulations, with cure and mold finish affecting surface |
| End of life | Clean scrap may be reprocessable under controlled limits | Cured network does not remelt; grinding or specialized recovery may be possible |
Flexibility is not a single number
Shore hardness does not define bending stiffness, elastic recovery, damping, creep or low-temperature behavior. Part thickness and shape may dominate. Compare force–deflection, compression set, fatigue and recovery at the intended temperatures using production-representative samples.
Where TPU needs special attention
Some polyester TPUs can lose properties under prolonged hot-water or humid exposure; polyether TPUs may improve hydrolysis resistance but change other properties. Processing moisture can also cause degradation or cosmetic defects. Use the exact supplier’s drying and exposure data, then validate the finished part.
Where thermoset rubber may earn its extra process steps
A selected rubber compound may be preferable for sustained compression, very high or low temperature, aggressive fluids or a specified sealing standard. The trade-off can include curing time, flash removal, tighter control of cure state and less straightforward scrap reuse. Rubber is not automatically slower or more expensive; compare the complete production route at the expected volume.
Cost comparison for the same functional requirement
Compare more than resin price:
- tool design, cavity count and mold-temperature system;
- cycle including cure or cooling;
- drying, post-cure, deflashing and secondary operations;
- scrap, rework and inspection;
- assembly or overmolding opportunities;
- validated service life and warranty risk; and
- material availability and change-control needs.
Selection workflow
- Define load, motion, temperature, chemicals, wear and lifetime.
- Choose candidate chemistries—not just hardness ranges.
- Review molding, assembly and tooling constraints.
- Mold representative samples using production conditions.
- Condition and test force, recovery, wear, seal and appearance.
- Compare total part cost at the same quality and lifetime.
Send the CAD model, service environment, load/deflection requirement, candidate compounds, annual volume and acceptance tests for DFM analysis. CKMOLD can review thermoplastic tooling options and prototype molded samples; request a quote for project-specific feedback.