TPU (Thermoplastic Polyurethane)

Overview

TPU (thermoplastic polyurethane) is the elastomer that bridges the rubber and thermoplastic worlds. Rubber-like elasticity, recovery, and abrasion resistance — processable on standard injection-molding and extrusion equipment used for ordinary thermoplastics. The result is a material that competes with vulcanized rubber for performance and with thermoplastics for manufacturing economy.

The defining TPU properties:

• Hardness range from 60 Shore A to 75 Shore D — covers essentially every elastomer application from very soft (eraser-firm) to very hard (rigid plastic-like).
• Highest abrasion resistance of any commercial elastomer. BASF and Lubrizol publish abrasion data showing TPU outperforming natural rubber, EPDM, and nitrile in standard Taber and DIN abrasion tests by factors of 3–10×.
• Excellent oil, fuel, and grease resistance — polyester TPU specifically is the workhorse for hydraulic and fuel hose.
• Wide temperature range — flexible to -40°C (polyether to -50°C), serviceable to 80–120°C.
• Recyclable and weldable — unlike vulcanized rubber, TPU scrap can be reground and remolded; parts can be ultrasonic, hot-plate, or solvent-welded.

The principal selection question is polyester vs polyether sub-family — both look similar, both process the same way, but they fail differently:

• Polyester TPU — highest mechanicals, best abrasion, best fuel/oil resistance. Vulnerable to hydrolysis in hot or humid environments. Fails over months to years in continuous hot water, steam, or tropical humidity.
• Polyether TPU — slightly lower mechanicals, slightly less abrasion-resistant. Excellent hydrolysis resistance. Standard for inflatables, cable jacketing in humid environments, medical tubing, anything that sees water for years.

A third aliphatic sub-family (Elastollan A-series, Estane ALR) uses aliphatic isocyanates instead of aromatic (MDI/TDI), producing water-clear, non-yellowing TPU at significant cost premium. The volume application is screen protectors and paint protection film for automotive.

Hardness — TPU’s defining design variable

TPU is sold and specified primarily by Shore hardness. BASF’s Elastollan hardness chart spans:

The hardness selection drives mechanical, thermal, and processing behavior:

• Tensile strength increases with hardness, from ~25 MPa at 60A to ~55 MPa at 75D.
• Elongation at break stays high across the range (~400–700%).
• Modulus spans three orders of magnitude — 5 MPa at 60A to 700+ MPa at 75D.
• Processing temperature climbs with hardness (170°C at 60A to 240°C at 75D).
• Compression set worsens with softness (soft grades acquire permanent set under sustained load).

Variant guidance — which TPU

• Polyester TPU (Elastollan C-series, Estane 2103/2355, Texin 245) — pick for abrasion-critical and oil-contact applications without hot water or steam exposure. Footwear soles, conveyor belts, hydraulic hose, industrial wheels.
• Polyether TPU (Elastollan 1100-series, Estane 2102, Texin 270) — pick for any service involving water, humidity, microbial exposure, or low temperature. Inflatables, cable jacketing in marine and tropical environments, medical tubing.
• Aliphatic TPU (Elastollan A-series, Estane ALR) — pick when optical clarity and UV stability matter together. Screen protectors, paint protection film, outdoor signage components.
• Flame-retardant TPU (Elastollan 1185AW, Estane FR) — pick for wire jacketing, transit-rail cable, telecom infrastructure where UL94 V-0 and low smoke toxicity are required.
• Medical TPU (Pellethane medical, Pearlthane medical, Elastollan SP) — pick for catheter components, wound dressings, validated medical fluid paths. USP Class VI compliance.
• FDM filament TPU — pick for 3D-printed flexible parts. Direct-drive extruder required.
• Glass-filled TPU — pick when toughness with rigid stiffness is required. Automotive structural and impact parts.

Machining notes

TPU is rarely machined — the material’s commercial value is in injection-molded or extruded geometry. When machining is necessary (prototype parts, small modifications, fixturing):

• Hard grades (Shore D and 95A+) machine like soft thermoplastics with sharp HSS or carbide, slow speeds, and air or mist coolant.
• Soft grades (under 90A) essentially cannot be conventionally machined — the workpiece deforms under cutter pressure. Cryo-machining with LN2 cooling stiffens the part enough to cut cleanly; specialty waterjet and die-cutting are the production alternatives.
• Bonding is good — solvent welding (THF, MEK) and adhesives (cyanoacrylates, polyurethane adhesives) bond TPU reliably. Hot- plate, ultrasonic, and high-frequency welding all work cleanly.

For shop fabrication of soft TPU stock:

1. Waterjet cutting for sheet stock
2. Die cutting for thin sheet (gaskets, seals)
3. Grinding for surface finishing
4. CNC milling only on Shore D grades; cryo for softer

Failure modes worth designing around

Polyester TPU hydrolysis is the dominant in-service failure mode when TPU is misspecified. Polyester TPU in continuous hot water, steam, or tropical humidity softens, becomes tacky, and loses tensile strength over months. The fix is grade selection: specify polyether TPU for any aqueous or humid service.

UV degradation of aromatic TPU — surface yellowing and embrittlement on outdoor exposure. Indoor and protected installations are unaffected; outdoor and UV-exposed applications require aliphatic TPU or pigmented compounds with UV stabilizers.

Compression set under continuous load — TPU recovers from short- term deformation but acquires permanent set under sustained compressive load over months. Static seals need either dynamic motion to recover the elastomer, live-loading with springs, or specification of low-compression-set grades (e.g. Elastollan 500-series).

Microbial attack on polyether TPU in chronically dirty environments (sewage, contaminated water) is documented in long-term applications. Less common than polyester hydrolysis failure but worth knowing for wastewater and septic system applications.

Cold cracking below -40°C for standard grades. Specialty cold-flex grades reach -60°C. Below this, TPU is brittle and elastomeric function is lost.

Applications by industry

• Footwear — the largest TPU application by volume. Outsoles (polyester), midsoles (polyester or polyether), ski boot shells, hockey skate shells, soccer cleat hardware. adidas FutureCraft 4D athletic shoes use SLS-printed TPU midsoles.
• Cable and wire — jacketing for transit-rail, mining, aerospace, consumer (USB, headphone), and industrial cables. Abrasion resistance and oil/chemical resistance are the drivers; flame- retardant grades for in-building wire.
• Hose — hydraulic hose covers, pneumatic tubing, water hose, layflat fire hose. Polyester TPU dominates the oil-contact applications.
• Automotive — interior trim, gaskets, weatherstripping, bumpers, fuel-system components, exterior body film (PPF / paint protection film), instrument panel skin.
• Medical — catheter components, wound dressings, ostomy bag films, peristaltic pump tubing. Polyether medical grades dominate.
• Consumer electronics — protective cases (smartphone, laptop), screen-protector film, charger cable strain reliefs, headphone cable jacketing.
• Sports and recreation — inflatable boat fabric, kayak skirts, ski-boot shells, hockey gear, golf ball cores, bicycle saddles.
• Industrial belting — conveyor belts, timing belts, V-belts in food processing and packaging where rubber belts shed particulate.
• Additive manufacturing — the dominant flexible FDM filament family. Custom orthotics (SLS TPU), small-batch flexible prototypes, gaskets, soft-touch grips.
• Inflatables — life rafts, marine bladders, inflatable boats, toy products. Polyether TPU for hydrolysis tolerance in marine service.