What is TPU injection molding? It produces flexible, abrasion-resistant parts across Shore A 60 to Shore D 70. Unlike rigid thermoplastics, TPU (Thermoplastic Polyurethane) combines rubber-like flexibility with thermoplastic processability — the material of choice for seals, cable jackets, wearable components, and overmolded grips.
What Is TPU
TPU's block copolymer structure alternates hard and soft segments, delivering a hardness range no single elastomer or rigid plastic can match on its own. That's what makes it useful from Shore A 60 soft grips to Shore D 70 structural components — all within the same processing window.
Polyester-based TPU resists oils, chemicals, and abrasion — right for industrial seals and mechanical parts. Polyether-based TPU stays flexible below −40°C and resists hydrolysis — preferred for wearables, medical tubing, and outdoor applications.
The one non-negotiable in processing: moisture control. TPU absorbs atmospheric humidity within hours of drum opening. Undried pellets flash to steam at barrel temperatures, causing splay and degraded mechanical properties. Desiccant drying to below 0.02% is required before every run.
Full materials library →Material Grades
Grade selection drives chemical resistance, low-temperature behaviour, UV stability, and regulatory status. We specify based
on what the part actually does — not what is simply available.
Superior resistance to oils, greases, and aliphatic solvents. Preferred for mechanical seals, wheels, and industrial components with high wear demands. Harder durometer range.
Stays flexible below −40°C. Resists hydrolysis and microbial degradation. Available in USP Class VI and ISO 10993 grades for medical device components and wearables.
High tensile strength and elongation at break. Cost-effective for cable jacketing, connectors, and electronics housings where UV stability is not a primary requirement.
No UV-induced yellowing. Correct choice for transparent windows, outdoor wearables, and clear covers where colour stability matters over the product’s service life.
How It Works
TPU is less forgiving than commodity plastics — moisture, shear rate, and cooling speed all directly affect surface finish and
mechanical performance.
Wall thickness, gate location, draft angles, and overmold interface checked before steel is cut. TPU minimum draft: 0.5° – 1° for Shore A <80.
Free with quoteDesiccant drying 80–110°C for 2–4 hr. Dewpoint monitored continuously. Target moisture <0.02% verified before barrel loading.
<0.02% moisture targetCavities machined to ±0.01mm via slow-wire EDM. Vented parting lines and polished ejection surfaces prevent sticking on soft grades.
±0.01 mm cavityBarrel 175–230°C, mold 20–60°C. Moderate injection speed — high shear causes thermal degradation in TPU. Scientific molding DOE on first article.
Scientific moldingFirst article on CMM (±0.002mm). Shore hardness verified per batch. Flexible parts measured under defined load to avoid deformation error.
CMM ±0.002 mmParts individually wrapped to prevent surface deformation in transit. Full dimensional report and material COA shipped with every order.
COA + dimension reportApplications
TPU's combination of flexibility, abrasion resistance, and processability spans four major sectors — each with distinct hardness and regulatory requirements.
Catheter shafts, IV connectors, wearable monitor housings, patient-contact overmolds. Polyether grades with USP Class VI and ISO 10993 data.
Watch straps, earphone sleeves, camera grips, case overmolds. Aliphatic TPU for UV-stable transparent covers. Shore A 70–85 for comfort ergonomics.
USB cable overmolds, strain reliefs, waterproof connector boots, industrial plug seals. Aromatic TPU for cost-effective high-volume cable runs.
Oil seals, conveyor elements, pneumatic actuator seals, protective boots. Polyester grades for oil and abrasion resistance in harsh environments.
Midsole inserts, binding components, protective padding. Shore D 40–55 for structural rigidity with impact absorption.
Design Guidelines
TPU requires different ejection strategies, draft angles, and gate geometry compared to rigid thermoplastics. Flexible materials grip polished steel harder — parts that eject cleanly at first article can stick after 5,000 cycles as micro-roughness accumulates.
The most common DFM failure we catch: insufficient draft on deep features combined with an overly polished cavity surface. For Shore A grades below 80, we routinely recommend VDI 18–24 texture instead of mirror finish.
Soft-grade TPU (Shore A 60–75) grips polished cavities. Add VDI 18–24 texture or increase draft to 1.5°+ on deep pull surfaces. Reduce ejection speed on first-article trials.
Draft ≥1° · VDI texture recommendedAlmost always underdried material. Verify with Karl Fischer titration on medical-grade runs — not timer-based drying alone. Target <0.02% moisture before every barrel loading.
Target <0.02% moistureDifferential cooling between cavity and core sides causes TPU to bow. Balance cooling channels within 15mm of cavity surface and hold uniform wall thickness across the geometry.
Balanced cooling · uniform wallsTPU bonds reliably to PA6 and PA66 without primers. PC requires plasma treatment or primer. ABS needs mechanical interlocks — chemical adhesion alone is unreliable for peel strength.
PA6/PA66 best · PC needs primeQuestions from engineers and procurement teams before sending a drawing.
Answered with actual process data from our production floor.
Shore A 60 to Shore D 70. Polyester grades cover the harder range with better chemical and oil resistance. Polyether grades stay flexible to −40°C and are the default for medical and wearable applications. Grade is confirmed at DFM review based on service conditions and any regulatory requirements.
TPU is hygroscopic — it absorbs atmospheric moisture rapidly. At barrel temperatures of 175–230°C that moisture turns to steam, causing splay marks, bubbles, and reduced mechanical properties in the finished part. We dry all TPU at 80–110°C for 2–4 hours in desiccant dryers and verify moisture below 0.02% before every run.
Yes. TPU bonds directly to PA6 and PA66 without primers in a standard two-shot or insert molding process. PC requires plasma treatment or a TPU-compatible adhesion primer. ABS needs mechanical interlocking — chemical adhesion alone is not reliable for consistent peel strength. Substrate compatibility is confirmed before tooling is committed.
TPU shrinkage ranges from 0.5% (harder Shore D grades) to 3.0% (soft Shore A grades). Most production molds are designed for 1–2% nominal shrinkage compensation. Soft-grade parts are more sensitive to wall thickness variation — uniform walls produce more consistent shrinkage than parts with abrupt geometry changes.
Yes. We run polyether-based TPU grades with USP Class VI and ISO 10993 biocompatibility data for medical device components and patient-contact applications. These programs require review of the selected production-site scope and specified lot traceability from material COA to finished part documentation. Cleanroom production is available for components with contamination-sensitive requirements.
Upload your 2D drawing & 3D file. Our engineers review DFM within two business day and return a quote — at no cost.
