1. Introduction

Polyurethane elastomers have been used in footwear, textile coatings, and medical devices for over six decades, making them one of the most mature PU material families. PU microcellular soles account for approximately 35% of the global athletic shoe sole market, valued for lightweight cushioning and abrasion resistance. TPU films for waterproof breathable apparel, medical dressings, and artificial skins have driven growth in the TPU film market, estimated at USD 4.5 billion globally in 2025. With the maturation of 3D-printed TPU and bio-based PU elastomers, new opportunities are emerging in custom orthotics and resorbable medical devices. This article reviews three representative applications.

2. Technical Features and Mechanism

Footwear PU microcellular elastomers are typically processed by reaction injection molding (RIM): polyester polyol reacts with MDI to form a thermoplastic PU, which is foamed and molded in a single step. Material density is 0.35-0.60 g/cm³, Shore A hardness 50-70, Akron abrasion ≤0.15 cm³/1.61 km, and flex life ≥100,000 cycles per GB/T 3903.1.

TPU films are produced by solution casting or melt extrusion at 10-50 μm thickness, offering water vapor transmission rates of 500-10,000 g/(m²·24 h) per GB/T 12704.2 and hydrostatic resistance of 5,000-10,000 mmH₂O. Medical-grade TPU must pass ISO 10993 biocompatibility (cytotoxicity, sensitization, irritation) and be free of phthalate plasticizer migration. Relevant standards: GB/T 3903.1 (shoe abrasion), ISO 20347 (occupational footwear), and ISO 10993 (medical device biocompatibility).

3. Application Case Study 1: Athletic Shoe Dual-Density PU Midsole

A sports footwear brand developed a dual-density PU midsole for running shoes. Two PU materials are co-injected in one shot: the upper layer (insole contact) uses Shore A 45 soft PU for cushioning, while the lower layer uses Shore A 60 firm PU for propulsion and abrasion resistance. The formulation employed polyester polyol (MW=2000) 100 phr, 1,4-butanediol 8 phr, MDI prepolymer (NCO=8%), and water as blowing agent at 0.5 phr. The midsole achieved density 0.45 g/cm³, resilience ≥45%, Akron abrasion 0.08 cm³/1.61 km, and no cracking after 120,000 flex cycles. After an 800 km running test, compression set was ≤8%, and weight was 20% lighter than an EVA equivalent. The midsole is used in the brand's marathon training line.

4. Application Case Study 2: TPU Waterproof-Breathable Apparel Laminate

An outdoor fabric mill laminated a microporous TPU film to polyester woven fabric for waterproof breathable shells. The TPU film is 15 μm thick, with moisture vapor transmission rate 8,000 g/(m²·24 h), hydrostatic head 8,000 mmH₂O, and ≥90% retention after 20 launderings. Pore sizes of 0.1-10 μm allow water vapor molecules through while blocking liquid droplets. The laminate was tested to GB/T 4744 (hydrostatic pressure) and GB/T 12704.2 (moisture vapor transmission), achieving class-3 waterproof performance. The fabric is used in mountain shells and ski wear. At 5,000 m altitude field testing, no condensation occurred inside the garment, and the fabric remained flexible at -30°C. Compared to ePTFE, TPU film reduces cost by 30% and is recyclable.

5. Application Case Study 3: Medical TPU Catheter

A medical device manufacturer uses medical-grade TPU for central venous catheters (CVC) and negative-pressure drainage tubing. The TPU formulation is Shore A 85, with tensile strength ≥35 MPa, elongation ≥500%, and adequate X-ray opacity. It passes ISO 10993-5 cytotoxicity and ISO 10993-10 sensitization/irritation tests, with ethylene oxide sterilization extractables ≤0.5%. The catheter inner diameter is 1.0-3.0 mm, wall thickness 0.2 mm, and no kink at a 5 mm bend radius. The product has obtained a medical device registration certificate and is used in tertiary hospitals. Compared to PVC, TPU catheters contain no DEHP plasticizer, offer better tissue compatibility, and can remain in place up to 28 days. DENSON develops color pastes compatible with medical TPU systems.

6. Key Selection Parameters and Usage Recommendations

Selection guidance: (1) Footwear PU should use polyester polyols for wear and oil resistance; choose polycaprolactone when hydrolysis resistance is critical. (2) Waterproof-breathable apparel requires microporous TPU, not nonporous TPU, for 5-10× higher MVTR. (3) Medical TPU must be sourced with biocompatibility reports and medical device master files. (4) PU color pastes for textiles and footwear must resist migration (150°C ironing for 3 min) and washing (50 cycles ΔE ≤2.0). Explore DENSON's consumer PU color paste portfolio.

7. Conclusion

Polyurethane elastomers embody biocompatibility, light weight, and precision molding across footwear, textiles, and medical devices. From running shoe midsoles to intravascular catheters, PU's processability and tunable properties continue to displace PVC and rubber. With the rise of 3D-printed TPU and bio-based PU, custom orthotics and resorbable medical PU are emerging growth frontiers. Dongguan DENSON Functional Materials Co., Ltd. provides stable coloration and functional colorants for consumer and medical PU applications.

8. FAQ

Q1: Which is more wear-resistant, PU soles or EVA soles?
A1: PU soles outperform EVA. PU Akron abrasion is typically ≤0.15 cm³/1.61 km versus 0.3-0.5 for EVA. PU density is 0.45 g/cm³ (heavier than EVA at 0.20) but offers higher resilience (45% vs 35%). PU soles suit outdoor and work boots for long wear life, while EVA suits lightweight casual shoes. Premium running shoes often combine "EVA midsole + PU outsole" for light weight and abrasion resistance.

Q2: Is a higher MVTR always better for TPU apparel film?
A2: MVTR must be balanced against hydrostatic resistance. Microporous TPU reaches 5,000-10,000 g/(m²·24h), but larger pores reduce hydrostatic head. Outdoor apparel targets 5,000-8,000 MVTR with ≥8,000 mmH₂O hydrostatic. Overly high MVTR films can "weep" under heavy rain. Nonporous hydrophilic TPU offers only 500-2,000 MVTR but extremely high hydrostatic resistance (≥20,000 mmH₂O), suited to extreme weather.

Q3: What advantages does TPU catheter have over PVC?
A3: Medical TPU contains no DEHP phthalate plasticizer, avoiding leaching-associated health risks. TPU is softer (Shore A 85 vs PVC Shore A 75-90), more tissue-compatible, and supports dwell times extended from 7-14 days (PVC) to 28 days. TPU also shows better X-ray visibility for clinical positioning. The trade-off is cost (2-3× PVC) and higher processing temperatures.

Q4: How to select PU color pastes for textile coatings?
A4: PU textile color pastes require: (1) compatibility with PU resin (solvent or waterborne), no flocculation; (2) migration resistance at 150°C ironing and high-temperature drying; (3) wash fastness (50 cycles ΔE ≤2.0); (4) Oeko-Tex Standard 100 compliance (no azo dyes, no heavy metals). Choose solventborne pastes for shoe/handwear coatings and waterborne pastes for apparel. DENSON offers dedicated PU-system color pastes.