TPU Injection Moulding: Thermoplastic Polyurethane Material Guide
Thermoplastic polyurethane (TPU) is the highest-performing flexible injection-moulding material in common use. It delivers a combination of high tensile strength, outstanding abrasion resistance, excellent oil and fuel resistance, and a wide hardness range — properties that no commodity TPE can match. Nordmould moulds TPU for orders from 100 pieces, across both ether-based and ester-based grades.
What are the mechanical and thermal properties of TPU?
TPU properties vary significantly with hardness and chemistry (ether-based vs ester-based). The table below gives representative values across the most common injection-moulding range.
| Property | TPU Shore 75A | TPU Shore 87A | TPU Shore 95A | TPU Shore 55D |
|---|---|---|---|---|
| Tensile strength | 25–40 MPa | 35–50 MPa | 45–60 MPa | 40–55 MPa |
| Elongation at break | 500–800 % | 400–600 % | 300–500 % | 200–400 % |
| Tear resistance | 60–100 kN/m | 80–120 kN/m | 100–150 kN/m | 120–180 kN/m |
| Compression set (22 h / 70 °C) | 15–30 % | 12–25 % | 10–20 % | 8–18 % |
| Abrasion resistance (DIN 53516) | 40–90 mm³ | 25–60 mm³ | 20–50 mm³ | 15–40 mm³ |
| Heat deflection temp (0.45 MPa) | 55–70 °C | 65–80 °C | 75–90 °C | 85–100 °C |
| Continuous service temp | −40 to 90 °C | −40 to 100 °C | −40 to 110 °C | −40 to 120 °C |
| Water absorption (24 h) | 0.5–2.0 % | 0.4–1.5 % | 0.3–1.2 % | 0.2–0.8 % |
| Density | 1.10–1.22 g/cm³ | 1.12–1.24 g/cm³ | 1.14–1.25 g/cm³ | 1.18–1.28 g/cm³ |
Ether-based TPU (TPU-E) offers better hydrolysis resistance and low-temperature flexibility than ester-based TPU (TPU-ES). Ester-based grades provide superior oil, fuel, and UV resistance. The choice between ether and ester chemistry should be determined by the service environment — Nordmould's DFM review covers this selection.
What are typical applications of TPU injection moulding?
TPU's combination of mechanical strength, flexibility, and chemical resistance places it in demanding applications where ordinary TPE would fail.
Industrial and automotive: Industrial wheels, conveyor scrapers, impeller liners, and hose connectors all exploit TPU's abrasion resistance. Automotive applications include dust boots, bellows, sealing strips, and flexible fuel-line connectors where oil and fuel resistance is required alongside flex durability.
Electronics and cable protection: Cable jackets, strain-relief boots, and flexible conduit connectors use TPU for its combination of flexibility, UV resistance (in stabilised grades), and flame-retardant options. Phone cases and screen protectors in moulded TPU have become a major consumer electronics application.
Medical and healthcare: Ether-based, ISO 10993-tested TPU grades are used for catheters, tubing, orthotic and prosthetic components, wearable health-monitor housings, and wound-care components. TPU's biocompatibility, sterilisability, and flexibility in thin walls make it a natural choice here.
Footwear: Midsoles, outer soles, ski boots, and hiking boot rand components use TPU extensively — its abrasion resistance, rebound, and colourability are hard to match with other injection-mouldable materials.
Sports and safety equipment: Protective pads, shin guards, goggle frames, and helmet liners use harder TPU grades (Shore 55D–80D) for energy-absorbing structural-flexible parts.
How is TPU processed in injection moulding?
TPU is more demanding to process than commodity plastics. Its hygroscopicity, relatively narrow processing window, and tendency to degrade if held too long in the barrel require attention during process development.
| Processing parameter | Ether TPU (Shore 80A) | Ester TPU (Shore 95A) | Hard TPU (Shore 60D) |
|---|---|---|---|
| Melt temperature | 190–220 °C | 200–230 °C | 210–240 °C |
| Mould temperature | 20–50 °C | 30–60 °C | 30–70 °C |
| Injection pressure | 50–100 MPa | 60–110 MPa | 70–120 MPa |
| Shrinkage | 0.5–1.5 % | 0.5–1.2 % | 0.4–1.0 % |
| Recommended draft angle | ≥ 2° per side | ≥ 2° per side | ≥ 1° per side |
Drying is non-negotiable: TPU absorbs moisture readily and must be dried to below 0.02–0.05 % moisture content before moulding. Inadequate drying is the single most common cause of defects in TPU parts — including splay, bubble formation, and reduced tensile strength in the moulded part.
Residence time: TPU degrades if held at melt temperature for extended periods. Purging the barrel between shots during machine stops, and sizing the barrel to achieve a residence time of 4–6 minutes or less, prevents thermal degradation.
Sink and warp: TPU's shrinkage of 0.5–1.5 % is moderate and relatively isotropic. Sink marks appear in thick sections; the same wall-uniformity rules applied to other plastics apply here — keep walls between 1.5–5.0 mm and avoid abrupt transitions. TPU is compliant enough to accommodate minor warpage in assembly, but structural parts with mating surfaces require careful gate placement.
Gate design: submarine and pin-point gates work well for TPU; cold slugs should be accommodated at the runner–gate junction to prevent cold material from entering the cavity. For transparent medical or consumer TPU, fan gates minimise shear-stress marks.
What grades and variants of TPU are available?
| Grade | Key feature | Typical use case |
|---|---|---|
| Ether-based, Shore 80A | Soft, hydrolysis-resistant | Medical seals, outdoor flexible parts |
| Ether-based, Shore 95A | Balanced mechanical properties | Cable strain reliefs, sports goods |
| Ester-based, Shore 85A | Oil & fuel resistant | Automotive seals, industrial hose |
| Ester-based, Shore 55D | Semi-rigid, high strength | Structural flexible brackets |
| Flame-retardant TPU (UL94 V-0) | Fire safety | Cable management, electronics |
| Medical-grade TPU (ISO 10993) | Biocompatible, sterilisable | Catheters, wearable sensors |
| Transparent TPU | Optical clarity with flexibility | Screen protectors, visual indicator windows |
| Aliphatic TPU | UV stable, non-yellowing | Outdoor consumer goods, automotive glazing |
Engineering-grade and specialty TPU compounds — including carbon-fibre-filled, electrically dissipative, and chemical-resistant grades — are available on request through Nordmould's material partner network.
What are the advantages and limitations of TPU?
Advantages:
- Outstanding abrasion resistance — one of the best among flexible plastics
- High tensile strength (25–60 MPa) compared with TPE grades of similar hardness
- Good oil, grease, and fuel resistance (especially ester-based grades)
- Excellent low-temperature flexibility, maintaining elasticity down to −40 °C
- Wide hardness range (Shore 60A to Shore 80D) from a single material family
- Available in transparent, food-contact, medical, and flame-retardant grades
- Fully thermoplastic and recyclable; no vulcanisation
Limitations:
- Hygroscopic: strict pre-drying is required; short barrel residence time must be managed
- More expensive per kilogram than commodity TPE or PP
- Ester-based grades are susceptible to hydrolysis in prolonged wet environments
- More difficult to process than TPE; requires tighter process control
- Limited service temperature above 120 °C (harder grades) — not suitable for under-bonnet temperatures above 130 °C
- Chemical adhesion in over-moulding onto rigid substrates is less reliable than TPE-on-PP; mechanical interlocks often required
When should you choose TPU over alternative materials?
Choose TPU over TPE when abrasion resistance is a primary requirement (TPU DIN abrasion volume is typically 3–5× better than equivalent-hardness SEBS), when oil or fuel contact is expected, or when tensile strength must exceed 20 MPa.
Choose TPU over silicone for most injection-moulded parts — TPU uses standard injection equipment, is lower cost, and offers better abrasion and tear resistance. Silicone wins for continuous service above 150 °C or for implant-grade medical parts.
Choose ether TPU over ester TPU when hydrolysis resistance matters — outdoor parts, parts in contact with water or steam, and medical devices. Ester grades offer superior oil and fuel resistance and are preferred for automotive and industrial seal applications.
Choose harder TPU (Shore 50D–80D) over flexible POM or semi-rigid PP when the part must simultaneously be stiff and flexible, absorb impacts elastically, and return to its original shape. POM and PP are stiffer but do not recover elastically after significant deflection.
Recyclability and sustainability
TPU is thermoplastic and fully reprocessable. Sprues, runners, and reject parts can be reground and reblended at up to 10–15 % without significant loss in mechanical properties in non-critical applications. Post-consumer TPU recycling is technically feasible, though collection and sorting infrastructure for TPU is less mature than for PP or HDPE. Chemical recycling of TPU (glycolysis or hydrolysis back to polyols) is an established industrial process, particularly in the foam industry, and is being extended to moulded-parts streams. Bio-based TPU grades with partially renewable polyol content are commercially available and can be sourced by Nordmould on request.
Send Nordmould your STEP file and service-environment requirements — our free DFM review will cover hardness selection, ether vs ester chemistry, draft analysis, drying protocol, and a written quote returned within one business day.
Frequently asked questions
What makes TPU different from other flexible injection-moulding materials?
TPU (thermoplastic polyurethane) combines rubber-like flexibility with exceptional abrasion resistance, high tensile strength, and good oil and fuel resistance. Where TPE is chosen for soft-touch feel, TPU is chosen when the part must survive friction, flex fatigue, or chemical contact. Nordmould recommends TPU for wheels, seals in oily environments, and structural flexible components.
Does TPU need to be dried before injection moulding?
Yes — TPU is hygroscopic and must be dried thoroughly before processing. Inadequate drying causes hydrolytic degradation during moulding, resulting in reduced molecular weight, splay defects, and poor mechanical properties in the finished part. Nordmould dries TPU at 80–100 °C for 2–4 hours as standard before every production run.
What Shore hardness grades of TPU are available?
TPU is available from approximately Shore 60A (very flexible) to Shore 80D (semi-rigid). The most common injection-moulding range is Shore 70A–95A. Harder grades (Shore 55D–80D) are used for semi-structural applications such as cable sheaths and industrial wheels. Nordmould selects the appropriate hardness during the DFM review.
Can TPU be over-moulded onto rigid plastics?
Yes. TPU can be over-moulded onto ABS, PC, nylon, and POM substrates, though chemical adhesion is less reliable than TPE-on-PP and often requires mechanical interlocks in the design. Nordmould evaluates bond strategy — chemical compatibility, interface geometry, and process sequencing — during the DFM review for all two-shot projects.
Is TPU suitable for food contact or medical applications?
Medical-grade TPU (ether-based, with biocompatibility testing to ISO 10993) is widely used in catheters, tubing, wound-care devices, and wearable sensor housings. Food-contact TPU grades meeting FDA 21 CFR 177.1680 and EU 10/2011 are also available. Nordmould can source certified grades — confirm compliance requirements during the DFM review.
What is the minimum order for TPU parts at Nordmould?
TPU injection moulding is available from 100 pieces. Tooling starts from €3,000. TPU resin costs more per kilogram than commodity plastics such as PP or ABS, but its combination of properties typically eliminates secondary assembly steps (e.g. separate rubber seals), offsetting the material premium at the system level.
How does TPU compare with PU cast (polyurethane casting) for prototyping?
Cast PU (polyurethane casting / RTV moulding) is suitable for prototypes and very small quantities (5–50 parts) without hard tooling investment. However, cast PU uses two-component thermoset chemistry and produces parts with slightly different properties than injection-moulded TPU. Nordmould's bridge tooling offers a faster route to production-representative TPU parts from 100 pieces.