A client once sent us a design for a wearable device housing. They’d spec’d rigid ABS. It cracked on the third drop test. After switching to TPU, it survived over fifty. That one material decision saved them months of costly redesign and a product launch delay.
TPU — short for Thermoplastic Polyurethane — is a flexible, rubber-like plastic that processes like a standard thermoplastic. It combines the elasticity of rubber with the strength and moldability of plastic. TPU sits in a hardness range of roughly Shore 60A to Shore 80D, so it can be soft and bendable or relatively stiff depending on the grade. It resists abrasion, oils, and repeated flexing better than most standard plastics — which is why it shows up in everything from shoe soles to medical tubing to cable jacketing.
That range of behavior is exactly what makes TPU tricky to pin down. It’s not quite rubber, not quite rigid plastic. So let’s break it down properly — starting with what’s actually happening inside the material.
What Are the Properties of TPU?
This question matters before you commit to a mold. Understanding the mechanical profile of TPU helps you decide whether it’ll survive your use case — or fail the moment a customer gets their hands on it.
TPU’s standout properties include excellent abrasion resistance, high elasticity, and solid chemical resistance to oils and greases. It stays flexible at temperatures as low as -40°C for many grades. Tensile strength typically ranges from 25 to 65 MPa depending on the grade. Unlike most rubbers, it melts and flows — so it can be injection molded, extruded, or even 3D printed. Shore hardness varies widely, which is why TPU feels soft in shoe soles but firm in industrial rollers.
Hardness and Flexibility: More Options Than Most People Realize
A Shore 70A grade feels almost gel-like under your fingers. A Shore 65D grade has a solid, slightly rigid feel — closer to stiff nylon than flexible rubber. This range is something many designers don’t fully grasp until they’ve worked across several grades.
For product designers, this means TPU isn’t a single decision — it’s a category. The right grade depends entirely on the forces your part will face. A protective case for electronics needs a very different flexural modulus than a hydraulic sealing gasket.
Thermal Behavior
Standard TPU grades handle service temperatures between -40°C and roughly 80–100°C. Some specialty grades push higher. But if your application runs continuously at 120°C or above, you need a serious conversation about material options before assuming any TPU grade will hold up long-term.
Abrasion and Chemical Resistance
This is where TPU genuinely earns its reputation. In abrasion resistance testing, it consistently outperforms natural rubber, neoprene, and most other thermoplastic elastomers (TPE). For parts that slide, rub, or roll repeatedly against surfaces — conveyor guides, cable grommets, wear strips — TPU lasts significantly longer.
Chemical resistance is strong against oils, fuels, and many greases. It struggles against concentrated acids, strong bases, and some ketones. Always verify against your specific chemical environment.
Processing Characteristics
TPU processes well in injection molding, though it requires careful temperature and pressure control. It flows at relatively low viscosity when molten — useful for thin walls and complex geometries. But it’s also sensitive to moisture before processing, which we’ll cover in depth shortly.
At Dimud, our engineering team reviews TPU grades during DFM analysis to flag flow issues, warpage risks, and gate placement concerns before a mold is cut. That upfront step has saved several clients from expensive tooling revisions. More on that process is available on our plastic injection molding services page.
What Properties Make TPU the Material of Choice Over Other Plastics?
“Why not just use rubber?” — it’s a real question, and the answer is about manufacturability. TPU gives you rubber-like performance und the processing flexibility of a thermoplastic. Here’s what that combination means in practice.
TPU is chosen over conventional rubber and many thermoplastic elastomers because it can be injection molded without vulcanization — the slow chemical curing step rubber requires. This cuts cycle time and cost significantly. TPU also bonds well to rigid plastic substrates in overmolding, enabling soft-touch grips, seals, and flexible sections within one part. It offers higher abrasion resistance than most elastomers, recyclable scrap, and tighter dimensional control — advantages hard to match with traditional rubber processing.
The Vulcanization Problem — and Why TPU Sidesteps It
Traditional rubber parts require vulcanization: heat and chemical crosslinking that creates their final mechanical properties. It’s slow, labor-intensive, and the output isn’t recyclable. TPU skips all of that. Melt it, inject it, cool it, eject it. Cycle times for smaller parts can run under a minute.
That’s not a trivial advantage in production. When you’re making 50,000 units a month — as some of our clients do — shaving 30 seconds off a cycle time adds up very quickly across a production year.
TPU Overmolding: One of Its Most Underused Advantages
One of TPU’s most practically useful traits is its adhesion to rigid substrates — ABS, PC, nylon — during Umspritzen. This lets engineers design products with soft grip zones, impact-absorbing sections, or watertight seals, all produced in a single manufacturing step.
We’ve worked on handles, device housings, and tool grips using this exact combination. Getting it right means controlling substrate temperature, hold pressure, and gate location precisely. A weak bond line rarely shows up in first-article inspection — it shows up after a product has been in the field for six months.
Dimensional Stability vs. Rubber
A flat rubber sheet cut from a slab holds tolerances in the ±1–2mm range as standard. An injection-molded TPU part can hold ±0.1–0.2mm without difficulty. For snap-fit features, assembly interfaces, or anything with a mating component, that dimensional control is genuinely critical.
Recyclability
Scrap TPU can be reground and reused. Thermoset rubber, once cured, cannot be remelted. In production environments, this reduces material waste and lowers per-part cost over time — not dramatically, but consistently.
Is Thermoplastic Polyurethane (TPU) Hygroscopic?
This one trips up a lot of product teams. They choose a great TPU grade, skip pre-drying, and then wonder why parts are coming out with surface bubbles, silver streaks, or degraded mechanical strength. The answer is yes — TPU absorbs moisture — and it matters more than most people expect.
Yes, TPU is hygroscopic. Before injection molding, TPU pellets must be pre-dried, typically at 80–100°C for 2–4 hours, reducing moisture content below 0.05% by weight. Inadequate drying causes hydrolytic degradation during processing: polymer chains break down, resulting in poor mechanical properties, surface defects, and reduced part life. Even freshly opened bags of TPU pellets can absorb enough ambient moisture to cause processing problems within a few hours in humid conditions.
What Happens at the Molecular Level
TPU is a block copolymer with alternating hard and soft segments. The soft segments — typically polyether or polyester polyols — have a natural affinity for water. Moisture doesn’t sit on the surface; it diffuses into the pellet bulk.
Heat that pellet to 190–220°C in an injection barrel and the absorbed water turns to steam. It reacts with urethane linkages in a process called chain scission — the polymer chains literally break apart. The part may look normal coming out of the mold. Its mechanical properties won’t be.
Polyester vs. Polyether TPU: Moisture Sensitivity Is Different
Polyester-based TPU has stronger intermolecular forces and better mechanical strength — but its ester bonds hydrolyze over time in the presence of water, even after processing. In humid or wet applications, parts made from polyester TPU can degrade noticeably within 12–18 months of field use.
Polyether-based TPU resists hydrolysis. It holds up in wet environments, humid climates, and applications with repeated water exposure. For medical tubing, outdoor cables, or consumer products that live near water, this distinction can mean the difference between a two-year lifespan and a ten-year one.
This is a selection criterion that’s easy to miss in generic material comparisons. It matters.
Practical Pre-Drying Guidelines
- Temperature: 80–100°C. Some grades specify 90°C exactly — check your supplier’s datasheet.
- Time: 2–4 hours minimum in a dehumidifying dryer. Forced-air ovens are less effective.
- Moisture target: Below 0.05% by weight before processing.
- After drying: Keep pellets in sealed hoppers or temperature-maintained containers. Open bins in a humid factory will undo the drying within an hour or two.
This is something our process engineers verify during production setup for every TPU job — it’s one of those small parameters with outsized impact on part quality.
When Should TPU Be Used?
The honest question is not “can TPU work here?” but “should it?” TPU has clear strengths and real limits. Knowing where it makes sense — versus where a different material actually serves you better — separates a good design from an expensive mistake.
Use TPU when your part needs flexibility combined with toughness: cable sheaths, protective enclosures, wearable components, grips, seals, flexible tubing. It excels in parts undergoing repeated flexing or impact without fracturing. Avoid TPU for parts exposed continuously above 100°C, in concentrated chemical environments, or where high rigidity is required. Most TPU grades are translucent to opaque, not optically clear — so reconsider if clarity is a design requirement.
Applications Where TPU Consistently Performs Well
Consumer electronics: Phone cases, earbud tips, cable strain reliefs, flexible button membranes. Drop resistance and tactile grip are exactly what consumers notice — and what most quality cable accessories deliver through TPU rather than cheaper PVC.
Medical devices: Non-implantable tubing, catheter components, peristaltic pump tubing, protective grips. Certain grades carry ISO 10993 biocompatibility testing. Medical-grade selection requires careful validation, but TPU is an established material in this space.
Footwear and wearables: Outsoles, watch straps, fitness tracker bands. The combination of abrasion resistance and flex is the core value driver here.
Industrial components: Conveyor belt components, drive rollers, wear strips, hydraulic seals. High-cycle, high-abrasion environments where TPU’s durability advantage over rubber compounds shows up clearly after 6–12 months of operation.
When TPU Is the Wrong Choice
If the part must maintain structural rigidity at 120°C under load, look elsewhere. If you need water-clear optical components, TPU won’t deliver without specialty grades that change the cost picture significantly. If cost dominates for a low-performance flexible part, standard TPE blends or PVC may be meaningfully more economical.
I’ve seen startups over-specify TPU for parts that needed nothing more than flexible PVC. The TPU version cost three times as much per kilogram, required tighter mold tolerances, and delivered no measurable benefit in the application. No one came out ahead.
Prototype Before Committing
If you’re uncertain, prototype physically. 3D-printed TPU prototypes give you a quick, tactile feel for how the material behaves before committing to tooling investment. We regularly recommend this step to clients deciding between two material options — it answers the question in days rather than weeks. Our prototype creation service supports exactly this kind of early-stage validation.
How Does TPU Differ from Silicone?
This comparison comes up constantly. Both materials are flexible, both appear in similar product categories, and both get grouped together as “soft materials.” But they behave very differently in production, in the field, and in your budget.
TPU and silicone are both flexible elastomers but differ fundamentally in chemistry and processing. Silicone is thermoset — it cures permanently and cannot be re-melted or recycled. TPU is thermoplastic — it injection molds on standard equipment and generates recyclable scrap. Silicone handles higher continuous temperatures (200°C+) and has better UV and ozone resistance. TPU offers superior abrasion resistance, higher mechanical strength, and lower raw material cost. The decision usually comes down to temperature range, chemical environment, surface feel, and manufacturing infrastructure.
Processing: Where the Biggest Practical Difference Lives
Liquid Silicone Rubber (LSR) is a two-component system requiring specialized injection equipment — heated molds, cold barrels, dedicated machines. TPU runs on standard thermoplastic injection molding equipment. If tooling infrastructure is already in place for thermoplastics, adding TPU is a straightforward process change. Adding LSR is a capital decision.
This doesn’t make silicone harder to work with — it makes it different, with higher setup costs. For small-batch or low-volume production, that infrastructure investment matters a lot. Our liquid silicone rubber injection molding service handles LSR specifically — the two processes really are distinct enough to run as separate capabilities.
Temperature Range: Silicone Wins Clearly
Silicone retains flexibility from -60°C to over 200°C continuously. Most TPU grades begin softening above 80–100°C under mechanical load. For anything near a heat source — oven seals, under-hood automotive components, lighting fixture housings — silicone is the correct material. There’s no workaround within standard TPU grades.
Abrasion Resistance: TPU Wins Clearly
Silicone has poor abrasion resistance. Silicone parts that rub against surfaces wear quickly. For any application involving mechanical contact, sliding friction, or repeated wear, TPU outperforms silicone by a significant margin and with a measurable difference in service life.
Surface Feel and Tactile Character
Silicone has a characteristic soft, slightly draggy feel that consumers associate with premium quality in many product categories. TPU can be formulated to be smooth or textured, but the tactile character is different — less tacky, more plasticky. Neither is objectively better. It depends on the experience you’re designing for.
Cost
TPU is generally less expensive per kilogram than silicone, and standard injection tooling is less expensive to build than LSR tooling. At volume, the unit cost difference between a TPU part and an equivalent LSR part is real — not always decisive, but real.
What Are the Main Types of TPU — and How Do You Choose?
Not all TPU is the same material. Selecting “TPU” without specifying the chemistry is like ordering “steel” without specifying grade or hardness. The underlying chemistry affects processing, long-term performance, and regulatory compliance.
TPU is broadly divided into polyester-based and polyether-based grades. Polyester TPU offers better mechanical strength, oil resistance, and abrasion resistance — suited for industrial and outdoor applications. Polyether TPU resists moisture and hydrolysis better, making it more appropriate for humid environments and medical uses. Polycarbonate-based TPU grades offer higher thermal stability. Further differentiation comes from hardness, additive packages (flame retardant, UV stabilizer, antimicrobial), and regulatory compliance for specific markets.
Polyester vs. Polyether: The Core Decision
Polyester TPU builds on ester linkages in the soft segment. These create stronger intermolecular forces — higher tensile strength and better abrasion resistance. The tradeoff: ester bonds hydrolyze over time in the presence of water. For outdoor or wet-environment applications, this manifests as degradation after 12–24 months of field use.
Polyether TPU uses ether linkages instead. These resist hydrolysis. They don’t break down in humid or wet conditions the same way. For medical tubing, outdoor cables, watch straps, or consumer products in regular water contact, polyether grades hold up significantly longer over the product’s actual service life.
This selection point deserves more attention than it typically gets in general material guides.
Flame Retardant Grades
Many TPU formulations include flame retardant additives for electronics housings, wire and cable insulation, and building products. These grades are tested to UL 94 standards — commonly V0 or V2 ratings. For consumer electronics enclosures and cable jackets, this isn’t optional — it’s a regulatory requirement in most export markets, including the US and EU.
When working through Materialauswahl with our engineering team, this is one of the first questions we raise for any consumer electronics application: which safety certifications apply, and does the material formulation support them?
Hardness Selection Reference
- Shore 60A–80A: Very soft, gel-like. Cushioning, medical grips, earbud tips, orthotic insoles.
- Shore 85A–95A: Medium flex. Most common range for footwear outsoles, protective cases, cable sheaths.
- Shore 40D–60D: Stiff but slightly flexible. Industrial rollers, structural flexible components, conveyor parts.
Going outside the range you actually need creates problems. Too soft, and the part deforms under load. Too stiff, and it loses the flex range or impact absorption you designed around.
Can TPU Be Injection Molded — and What Should You Watch For?
Yes, TPU injection molds cleanly. But it has quirks that catch teams off guard if they’re new to the material. Processing it without understanding those quirks produces surface defects, weak weld lines, and parts that don’t match their specified properties.
TPU processes on standard injection molding equipment at barrel temperatures of 180–220°C and mold temperatures around 20–50°C. Key requirements: mandatory pre-drying (80–100°C for 2–4 hours), low back pressure to prevent shear degradation, and careful gate design since flexible parts show gate marks more prominently than rigid ones. Residence time in the barrel should be kept short. Soft grades need optimized ejection systems — thin, flexible parts can stretch or tear on ejection if draft angles and ejector placement aren’t designed for the material’s behavior.
Draft Angles for Flexible Parts
With rigid plastics like ABS or PC, a 0.5–1° draft angle is standard. With soft TPU — especially Shore 85A and below — you can sometimes use less draft because the part flexes on ejection. But that flexibility cuts both ways. A part that peels off a core can tear if wall thickness or gate location isn’t right.
The most common mistake we see in designs coming in for DFM review: zero draft on internal features with tight tolerances, combined with a soft TPU spec. The mold works on shot 1. By shot 200, there’s a wear pattern developing. By shot 2,000, dimensions drift. Our DFM analysis service specifically catches this for flexible material tooling — it’s preventable with upfront review.
Überlegungen zur Wanddicke
TPU flows reasonably well in thin walls, but below about 0.6mm, fill issues and surface defects become common in most standard grades. Uniform wall thickness also matters more with TPU than with rigid plastics. Differential cooling in variable-wall sections creates warpage that a flexible material actually retains — unlike a rigid part, it can’t be pushed flat after ejection.
Weld Lines in Flexible Parts
Weld lines in TPU parts are proportionally weaker than in most rigid materials. Avoid placing weld lines in areas that will undergo repeated bending or cyclic stress. Gate location during mold design should account for where weld lines form and whether those positions coincide with high-stress geometry.
At Dimud, we run mold flow simulations before finalizing gate placement on TPU parts. It’s not a formality — it directly impacts long-term part quality. If you’re evaluating a manufacturing partner for TPU injection molding and weld line location isn’t being discussed during mold design, treat that as a flag.
Schlussfolgerung
TPU earns its place in designs where rubber is too expensive to process and rigid plastic won’t flex enough. It’s tough, abrasion-resistant, moldable, and versatile across a wide hardness range. It also has real limits: temperature ceiling around 100°C, moisture sensitivity before processing, and hydrolysis risk in polyester grades exposed to water over time.
The material choice is half the equation. The other half is how it’s processed and how the mold is engineered around it. If you’re working on a product that involves TPU — or you’re still deciding whether TPU is the right call — our engineering team at Dimud is available to review your design. We’ve run a lot of TPU through our tools. We know where it performs and where it doesn’t.
