TPU

What Is TPU Injection Molding?

Thermoplastic polyurethane (TPU) is a thermoplastic elastomer that combines the elasticity and resilience of rubber with the processability and recyclability of a true thermoplastic. Chemically, TPU is a block copolymer built from alternating hard segments — a diisocyanate reacted with a short-chain extender — and soft segments based on a long-chain polyol. The ratio of hard to soft segments controls the final durometer, so one polymer family spans the range from flexible soft-touch grades around Shore A 60 to semi-rigid engineering grades near Shore D 55. This tunability is why TPU appears in everything from phone cases to industrial seals.

In injection molding, TPU runs on conventional screw injection machines, which makes it a practical replacement for thermoset rubber in many sealing, cushioning and wear applications. Because TPU is a thermoplastic, sprues and runners can be reground and reused, cycle times are far shorter than vulcanization-based rubber molding, and no curing agents or release chemistry are involved. For OEMs that currently mold or bond rubber components, switching to TPU typically simplifies the supply chain and lowers the per-part cost once tooling is amortized over the program volume.

TPU grades are broadly divided into polyester-based and polyether-based families. Polyester TPU offers superior oil, grease and solvent resistance plus higher tensile and tear strength, while polyether TPU delivers better hydrolysis resistance, low-temperature flexibility and microbial resistance. Grade selection therefore depends on the service environment as much as on the mechanical requirements. MOLDITQUICK works with both families and helps customers select the correct durometer and backbone for the application. For an overview of our molding capabilities, see our injection molding service page.

Key Properties of TPU

Property	Typical Value	Why It Matters
Hardness	Shore A 60 – Shore D 55 (grade-dependent)	Covers soft-touch grips through semi-rigid structural parts.
Tensile strength	≈ 20 – 60 MPa	High strength for an elastomer; carries load without permanent set.
Elongation at break	≈ 300 – 600%	Recovers from repeated flexing and impact without cracking.
Abrasion resistance	Excellent — very low Taber wear loss	Outwears rubber and most TPEs in sliding-contact service.
Low-temperature flexibility	Retains flexibility down to about −40 °C	Seals, boots and cables keep working in cold environments.
Oil and grease resistance	Good to excellent (polyester grades better)	Resists fuels, oils and greases in automotive and industrial use.
Density	≈ 1.10 – 1.25 g/cm³	Lightweight compared with rubber; relevant to part weight budgets.

Processing Parameters We Control

TPU is hygroscopic: it absorbs moisture from the atmosphere, and even small amounts of water cause hydrolysis and visible surface defects at melt temperature. Drying discipline is therefore the single most important processing control. The processing windows below are standard industry values; exact settings are fine-tuned for each grade, hardness and part geometry during mold trials.

Parameter	Typical Range
Pre-drying	80 – 100 °C for 2 – 4 h, dew point ≤ −40 °C
Melt temperature	190 – 220 °C (hardness- and grade-dependent)
Mold temperature	20 – 40 °C
Injection speed	Medium to fast; adjusted to avoid melt fracture and flow marks
Mold shrinkage	≈ 0.3 – 1.5% (harder grades shrink less)
Back pressure	Low to moderate, typically 5 – 15 MPa equivalent

Melt temperature should stay below roughly 230 °C for most grades to avoid thermal degradation and discoloration. Harder TPU grades generally process at the upper end of the melt range, while soft grades need gentler screw speeds to avoid excessive shear heating. Because TPU flows well at moderate temperatures, gating and venting can follow standard elastomer practice.

Common Applications

• Soft-touch grips and handles: power tools, personal care appliances, hand tools and consumer electronics use TPU overmolds for grip, damping and comfort.
• Seals, gaskets and O-rings: polyester TPU resists oils and hydraulic fluids in industrial sealing applications where rubber wears out quickly.
• Cable jackets and connectors: flexibility, abrasion resistance and flame-retardant grades suit cable, plug and connector overmolds.
• Footwear components: soles, cleats and cushioning elements exploit TPU's wear resistance and energy return.
• Protective covers and cases: phone cases, camera housings and instrument covers need drop resistance combined with a soft feel.
• Casters, wheels and rollers: TPU tires and treads outlast many elastomers under load.

Design Guidelines for TPU Parts

• Uniform wall thickness: keep walls between roughly 1.5 and 4 mm and avoid abrupt thickness changes to prevent sink marks and uneven shrinkage.
• Generous radii: use corner radii of at least 0.5 × wall thickness; TPU is notch-sensitive under repeated flexing.
• Draft angles: allow 1 – 3° of draft, although flexible parts often strip from the mold with less because TPU flexes during ejection.
• Shrinkage compensation: account for 0.3 – 1.5% mold shrinkage and verify with prototype tooling when mating surfaces carry tight tolerances.
• Overmolding: when TPU is molded over rigid substrates such as ABS, PC or nylon, design mechanical interlocks and verify adhesion with the selected grade combination.
• Gate placement: locate gates to keep knit lines out of high-stress areas; edge gates and submarine gates are common for elastomeric parts.

Common Defects and Prevention

• Bubbles and water marks (splay): caused by moisture in the pellets. Dry at 80 – 100 °C to a dew point of −40 °C and keep resin sealed between runs.
• Flow marks: surface streaking from low melt temperature or low injection speed; raise melt temperature and increase injection speed.
• Short shots: incomplete fill in thin sections; enlarge gates, improve venting, or raise melt and mold temperature.
• Flash: overflow at the parting line from excessive injection pressure or worn tooling; check mold fit, clamping force and venting.
• Voids and sink marks: appear in thick sections as the part cools; redesign with uniform walls or add cooling channels.

TPU vs. Other Elastomer Materials

TPU is most often compared with two alternatives: general-purpose thermoplastic elastomers (TPEs) and thermoset rubber. Styrenic TPEs (SEBS-based) are cheaper and process even more easily, but they have lower abrasion resistance, lower tear strength and poorer oil resistance than TPU. For parts that see sliding contact, chemical exposure or repeated flexing, TPU is the more durable choice despite the higher material cost.

Compared with thermoset rubber (EPDM, NBR, silicone), TPU offers faster cycle times, recyclability and better abrasion resistance, but a lower continuous service temperature — most TPU grades are rated to roughly 80 – 90 °C continuous, whereas some rubber compounds tolerate 120 °C or more. For soft-touch, sealing and wear applications below that temperature ceiling, TPU frequently wins on total cost while matching rubber performance in the field.

MOLDITQUICK Capabilities

MOLDITQUICK operates in-house injection molding with molds manufactured in our own tool room, giving us direct control over the processing variables that determine TPU part quality — drying, melt temperature, mold temperature and cycle time. We support TPU overmolding onto rigid plastic substrates, multi-cavity tooling for high-volume elastomeric parts, and secondary operations such as trimming, assembly and packaging.

Every project starts with a DFM review of wall thickness, gate placement and shrinkage so the mold is right the first time. Send us your part file or drawings for an evaluation, or request a quotation through our online quote form — we will confirm grade selection, tooling strategy and piece price before you commit to production.