A structured briefing for R&D engineers and manufacturing technologists: why one and the same material class can be as soft as an eraser and as hard as a boot sole — and how to avoid choosing the wrong grade.
Definition
Thermoplastic polyurethane (TPU, thermoplastic polyurethane) is a linear block copolymer in which "hard" and "soft" segments alternate. Under the ISO 18064 classification it belongs to the family of thermoplastic elastomers (TPE) and is designated TPU. Unlike cast (thermosetting) polyurethanes, TPU does not cross-link during processing: it can be melted, molded and reprocessed like an ordinary thermoplastic. It is precisely this combination — the elasticity of rubber plus the processability of plastic — that has made TPU one of the most versatile engineering elastomers.
Chemistry and structure
Picture a chain assembled from two kinds of links alternating in blocks. The first — the hard segments — are formed by the reaction of a diisocyanate (most often MDI) with a small chain-extender molecule (for example, 1,4-butanediol). The second — the soft segments — are long, flexible polyol macromolecules (polyester- or polyether-based). The hard blocks tend to gather together and form physical "junctions" — crystalline domains that act as temporary cross-links. The soft blocks between them stretch like little springs.
When the material is heated, the hard domains "melt" and the chains flow — TPU can be cast or extruded. When it cools, the domains reassemble and the part regains its elasticity. This is a fundamental difference from classic vulcanized rubber, where the cross-links are chemical and irreversible: rubber cannot be remelted, but TPU can.
The ratio of hard to soft segments determines the hardness. More hard blocks means a harder material (closer to 95A and even into the Shore D range). More soft blocks means a more flexible one (80A and below). That is why TPU grades are named by hardness: soft and medium grades by Shore A (80A, 90A, 95A), hard grades by Shore D (55D, 65D). Glass-fiber reinforcement shifts the material even further into the Shore D range.
Properties
| Parameter | TPU 85A | TPU 95A | Method | Note |
|---|---|---|---|---|
| Hardness | 85 Shore A | 95 Shore A | ISO 868 | the defining parameter of the grade |
| Density | 1.12 g/cm³ | 1.20 g/cm³ | ISO 1183 | typical for the class |
| Tensile strength | 35–45 MPa | 45–55 MPa | ISO 37 | typical for the class |
| Elongation at break | 500–650% | 400–550% | ISO 37 | very high elasticity |
| Tear resistance | 60–90 kN/m | 90–140 kN/m | ISO 34 | typical for the class |
| Abrasion resistance | 25–40 mm³ | 20–35 mm³ | ISO 4649 | one of the best among elastomers |
| Service range | −40…+80°C | −40…+90°C | — | higher for short periods |
The values in the table are typical for the TPU class of the corresponding hardness, not the datasheet figures of a specific grade. Confirm the exact parameters for a specific formulation against the TDS and on trial molding.
Note two rows that make TPU unique: elongation at break (hundreds of percent — the material stretches to several times its length) and abrasion resistance. In abrasion resistance, polyester TPU outperforms most rubbers and even many engineering plastics — which is exactly why it is used for rollers, drive belts and protective tool sleeves.
Polyester or polyether: two "characters" of one class
The soft segment determines the conditions in which TPU will feel comfortable. This is the most important choice, and one that is often underestimated:
- Polyester TPU — higher mechanical performance, better resistance to abrasion, oils and hydrocarbons. Its weakness is hydrolysis: in hot water and humid climates the polyester chain gradually breaks down.
- Polyether TPU — better hydrolytic stability, low-temperature behavior and resistance to microorganisms (fungi). It is inferior to polyester in abrasion and oil resistance.
- Polycaprolactone TPU — a compromise option combining part of the advantages of both, but more expensive.
A fact that surprises many: two grades with the same "85A" figure can behave in opposite ways in a warm, humid environment simply because one uses a polyester polyol and the other a polyether. That is why Shore hardness is a necessary but insufficient characteristic for selection.
How it is produced
TPU is synthesized by polyaddition: a diisocyanate reacts with a mixture of polyol and chain extender. There are two main routes — the prepolymer route (a prepolymer is prepared first, then the chain is extended) and one-shot (all components are mixed simultaneously). The reaction is run in a reactor or directly in a reactive extruder; the finished melt is pelletized.
The first polyurethanes were synthesized by Otto Bayer and his team at IG Farben in 1937 — according to a common account, partly to circumvent DuPont's patents on polyamide (nylon). Historically, polyurethane and nylon are "cousins," born of the competition for one and the same fiber market. Thermoplastic polyurethanes as a distinct class appeared later, in the 1950s–60s, and have since become the standard wherever "rubber that can be cast" is needed.
Finished TPU pellets must always be dried before processing — the material is hygroscopic, and moisture at high temperatures degrades the chain (more on this in the limitations section). TPU is processed by injection molding, extrusion (films, hoses, profiles, cable insulation), blow molding and, in recent years, 3D printing (filament for FDM and powder for SLS).
Typical applications
- Footwear. Soles, spacers, cushioning elements, studded heel plates. TPU holds its shape, does not "go soft" and resists abrasion excellently.
- Industrial rollers and wheels. Polyurethane treads on forklift wheels, roller tables and conveyors — wherever rubber wears out quickly.
- Drive and conveyor belts. High strength and flex resistance.
- Flexible hoses and tubing. Pneumatics, low-pressure fuel and hydraulic lines (polyester TPU is oil-resistant).
- Cable insulation and jacketing. Flexible cables subjected to bending and abrasion (robotics, spiral cables).
- Protective sleeves and dampers. Tool housings, bumpers, seals, vibration dampers.
- Sporting goods and wearables. Straps, overlays, protective elements, 3D-printed insoles.
Comparison with class neighbors
| Property | TPU | TPE-S (SBS/SEBS) | Vulcanized rubber | Flexible PVC |
|---|---|---|---|---|
| Abrasion resistance | very high | medium | high | low |
| Oil resistance (polyester) | high | low | depends | medium |
| Remelting capability | yes | yes | no | yes |
| Low-temperature performance | −40°C | down to −60°C | depends | worse |
| Plasticizers in composition | no | no | no | yes (they migrate) |
Conclusion: TPU wins where high mechanical performance, resistance to abrasion and oils, and thermoplastic processability are all required at once. SBS/SEBS compounds (the Exaflex® family also covers them) are often cheaper and softer, but fall short in abrasion and oil resistance. Flexible PVC is inexpensive but contains plasticizers that migrate over time — for skin or food contact this is often undesirable.
Designation in industry
TPU hardness is specified on the Shore scale: Shore A for soft and medium grades (ISO 868, ISO 7619-1), Shore D for hard ones. A practical rule applies here: up to ~95A hardness is read on Shore A, beyond that it switches to Shore D. The Shore A scale cannot exceed 100 and "compresses" near its ceiling, so it loses resolution. At the transition point the scales join: 95A ≈ 45D. Reference feel: 80A is like a bicycle tire, 95A is like a skate wheel, 65D is already a hard part, almost like a structural plastic. The A↔D relationship is nonlinear: 65D corresponds to about 99A — close to the ceiling of the scale (the A scale does not go above 100), and hard grades are measured on Shore D. In general, unfilled TPUs reach ~80–85D, glass-filled and reinforced ones higher.
The full material designation under ISO 1043 / ISO 18064 for the thermoplastic elastomer family is TPU; sometimes an index for the polyol type is added: ester (polyester) or ether (polyether). Technical specifications may include the abbreviations TPU-ARES (aromatic hard segment + polyester polyol) and TPU-ARET (aromatic + polyether), where the letters encode the segment types per ISO 18064.
Limitations worth knowing in advance
TPU is a powerful material, but it has honest limits, and a responsible selection starts precisely with them:
- Hydrolysis of polyester grades. In hot water, steam or constant high humidity, polyester TPU gradually loses strength. For such conditions, choose a polyether grade.
- Temperature ceiling. Continuous service is usually up to ~80–90°C; at higher temperatures the elastomer softens. Hot zones require other classes of material.
- Hygroscopicity. Undried pellets give bubbles, silver streaking and a drop in strength during molding — drying is mandatory.
- Sensitivity to UV and ozone (for some grades) — outdoor use requires stabilization.
- Sticking in the mold and to the screw. Soft grades tend to "stringing" — appropriate settings and mold design are needed.
- Not for continuous contact with concentrated acids/alkalis and certain solvents.
What to check before a production launch
- Pellet moisture. Dry according to the recommended regime (typically 70–90°C for several hours) and monitor moisture — this is more critical for TPU than for many other thermoplastics.
- Polyol type for the environment. Polyester or polyether — cross-check against the real service conditions (humidity, temperature, oil contact).
- Hardness on the finished geometry. The Shore value of a specimen and of a thin-walled part may feel different — verify on the actual product.
- Compression set. For seals and dampers — assess how much the part "remembers" compression.
- Flex and fatigue behavior. For belts, hoses and cables — cyclic testing across the operating temperature range.
- Abrasion in real friction pairs. The laboratory ISO 4649 is a reference, but the final word rests with a real-world test.
- Batch stability and color. For visible parts — shade control between batches.
Material Wizard grades in this category
Material Wizard supplies thermoplastic polyurethanes under the Exaflex® brand — a range by hardness from soft 80A to hard grades in the Shore D zone (Exaflex® TPU 55D and 65D-EF), as well as glass-filled LGF30. Grade selection depends on the environment (humidity, oils, temperature), part geometry and processing method.
Exaflex® TPU 80ASoft thermoplastic polyurethane · high elasticity · dampers, flexible partsRequest supply terms → Exaflex® TPU 90AVersatile hardness · belts, hoses, cable insulationRequest supply terms → Exaflex® TPU 95AHard wear-resistant polyurethane · rollers, soles, loaded partsRequest supply terms → Exaflex® TPU 55DHard polyurethane, Shore D zone · structural parts, high rigidityRequest supply terms → Exaflex® TPU 65D-EFHardest grade, ~65D · maximum rigidity and dimensional stabilityRequest supply terms → Exaflex® TPU LGF30Long-glass-fiber reinforced TPU · increased rigidity and dimensional stabilityRequest supply terms →All Exaflex® grades can be purchased with delivery across Ukraine. The price depends on hardness, polyol type, batch volume and lead times — check with a specialist: we will suggest a grade for your specific environment and current availability. If you have a sample or specification from another manufacturer, we will select a comparable material made to our own formulation.
5 expert questions before choosing TPU
1. In what environment will the part operate — dry, humid or hot water?
This determines the choice between polyester and polyether polyol. A mistake here is the most common cause of premature part failure through hydrolysis.
2. Will there be contact with oils, fuel or hydrocarbons?
If so, lean toward a polyester grade — it is considerably more resistant to swelling in oils.
3. What hardness is actually required — and has the geometry been taken into account?
A thin wall in 95A feels harder than a massive part of the same grade. Shore is the starting point, not the final one.
4. Does the part operate statically or under continuous flexing/impact?
For dynamic use, fatigue durability and tear resistance are critical, not just tensile strength.
5. How will the part be processed — by molding, extrusion or 3D printing?
The method dictates the requirements for flow and drying, and hence the choice of a specific grade.
FAQ
How does TPU differ from ordinary rubber?
Rubber is vulcanized — its cross-links are chemical and irreversible, so it cannot be remelted. TPU holds its shape thanks to physical "junctions" of hard segments that melt on heating. This makes TPU a thermoplastic: it can be molded, extruded and reprocessed while retaining rubber-like elasticity. In abrasion and oil resistance, polyester TPU often outperforms ordinary rubber.
What does a hardness of 80A, 95A or 65D mean?
This is hardness on the Shore A scale. 80A is a soft, flexible material (roughly like an eraser or a bicycle tire tread), 95A is hard and resilient (like a skate wheel). The higher the number, the harder the material. Soft and medium grades are measured on the Shore A scale, hard ones (from ~55D) on Shore D: up to ~95A this is Shore A, beyond that it switches to Shore D.
Why must TPU be dried before processing?
TPU is hygroscopic — it absorbs moisture from the air. At processing temperatures, moisture reacts with the polymer chain and breaks it (hydrolysis in the melt). The result is bubbles, silver streaking on the surface and a drop in mechanical properties. That is why the pellets are dried before molding or extrusion, usually at around 70–90°C for several hours.
Polyester or polyether TPU — which to choose?
If the part will operate in a humid, hot environment or contact hot water — polyether (better hydrolytic stability, low-temperature behavior and fungus resistance). If the priority is mechanical performance, abrasion and oil resistance — polyester. This decision matters more than the hardness figure itself.
Can TPU be 3D printed?
Yes. TPU is available as filament for FDM/FFF printing and as powder for SLS. For flexible grades in FDM, a direct filament feed path and a moderate print speed are important. SLS technology makes it possible to print lattice structures with variable density — this is exactly how modern insoles and soles are made.
Material Wizard (Derazhnia, Kharkiv) — a Ukrainian supplier of engineering polymers with its own technical material selection. Check with a specialist — we will suggest a TPU grade for your specific task and support the trials. See also: Exaflex® TPU catalog · carbon-fiber reinforcement in polyamides · PPA polyamide for high temperatures.