A seal that leaks, a bumper that does not absorb the impact or an elastic stop that deforms permanently are almost never problems that can be solved by looking only at the Shore value. To understand how to choose the hardness of industrial TPU, you need to start from the component's real function: how it is loaded, how many cycles it performs, in which environment and with which assembly constraints.
TPU, thermoplastic polyurethane, makes it possible to produce flexible parts with an interesting balance of elasticity, abrasion resistance and processability. But there is no "best" grade in absolute terms. A lower hardness favours deformation and grip; a higher one improves support, local resistance and geometric stability. The right choice comes from a compromise between these needs, not from an isolated number on a datasheet.
How to choose industrial TPU hardness based on function
The first question is not "what Shore hardness do we need?", but "what does the part have to do?". A component that has to seal between two surfaces requires controlled compression and the ability to follow small irregularities. An anti-vibration foot must dissipate part of the energy without collapsing under static weight. A cable grommet has to flex repeatedly without tearing. A roller, wheel or slider, on the other hand, must keep a reasonably stable profile under load and resist wear.
In practice, hardness must be matched to the mode of stress. In compression, a soft TPU can conform well but risks being excessively crushed. In bending, an overly rigid material concentrates stress in thin sections. In abrasion, a higher Shore value can help, but the material formulation, the roughness of the counterface and the presence of contaminants also count.
It is useful to define four operating conditions from the outset: maximum load, permissible deformation, expected number of cycles and operating temperature. Without these data, the hardness value remains an approximation.
Shore hardness: reading the scale correctly
For industrial TPU the Shore A scale is often used, suited to the more flexible elastomers. Values such as 70A, 85A or 95A indicate progressively harder materials, but they do not directly describe the stiffness of the final component. Geometry, thickness, print orientation and internal structure can drastically change the perceived behaviour.
A thin-walled component in 95A TPU can turn out to be more flexible than a solid block in 85A TPU. Likewise, a long, narrow tab concentrates bending at its base even if the material is relatively hard. Hardness is therefore a property of the material, whereas mechanical response is a property of the material-geometry-process system.
As a design reference, a TPU of around 70A–80A is recommended when high compressibility, surface grip or a soft contact is needed. The 85A–90A range is often a balanced choice for guards, flexible joints, technical grips and components subject to moderate bending. Towards 95A and above, TPU retains functional flexibility but is better suited to elements that must bear loads, resist wear or keep a more defined shape.
These ranges serve to guide the initial selection. They do not replace a test on the part, especially when the component is part of a mechanical assembly or has safety and durability requirements.
Load, deformation and elastic recovery
The most reliable criterion for choosing industrial TPU hardness is to measure how much deformation the component must withstand and what recovery it must guarantee after unloading. A buffer designed to compress by 10% works under very different conditions from an elastic hook that opens repeatedly by 40%.
When the part stays compressed for long periods, permanent set comes into play. A very soft TPU may be ideal for achieving the initial contact force, but after many hours or cycles it may not fully recover its shape. In sealing, support or damping applications, behaviour over time must be assessed, not just the first assembly.
The speed of loading also changes the response. TPU has viscoelastic behaviour: subjected to a rapid impact it can appear stiffer than under slow compression. For this reason a bumper designed to protect moving equipment must be assessed under real dynamic conditions, not solely with a manual test on the bench.
Temperature completes the picture. In the cold, flexibility can decrease, while in the heat a part can become softer under load. If the component operates near motors, electronic equipment, refrigerated environments or outdoors, the temperature range should be stated in the technical request from the start.
Geometry can change more than hardness
Before moving to a softer TPU, it is often worth checking whether the geometry is imposing excessive stiffness. Lightening a section, increasing the free length of a tab, adding fillet radii or changing the point of constraint can produce a more controllable improvement than changing the material alone.
Transition areas between rigid and flexible parts deserve particular attention. Sharp corners, sudden thin walls and holes close to an area subject to bending are points where stresses concentrate. A low-hardness TPU does not eliminate this problem: it may simply mask it during the first cycles.
For compressed elements, shape is just as decisive. A wide surface distributes the load, whereas a narrow rib concentrates it and can lead to crushing or lateral instability. If a progressive response is needed, a geometry with variable sections or purpose-designed cavities can be more effective than choosing an extremely soft material.
Additive technology and print orientation
In additive manufacturing, TPU performance also depends on the chosen process. Technology and print parameters influence surface finish, anisotropy, tolerances and behaviour in thin areas. For a flexible component intended for a run or final use, it is not enough to validate the shape: you need to validate the part produced with the intended technology.
Orientation should be defined according to the main load direction. A clip or flexible hinge should be oriented so that repeated stresses do not act at the most critical point of the layering. For sealing surfaces and mating seats, the achievable roughness and any required post-processing must also be considered.
Tolerances call for a practical approach. TPU can deform during insertion and recover, but that does not mean every interference is acceptable. A fit that is too tight can generate continuous stress, make assembly difficult or accelerate stress relaxation of the material. For assembled components, it is worth defining a functional test with the real counterpart.
A practical method for finding the right grade
To reduce iterations and costs, the choice can proceed through targeted samples. Start from a TPU grade consistent with the function, produce a small test batch and check behaviour in the actual assembly. Many variants are not necessarily needed: comparing two adjacent hardnesses, keeping geometry and process constant, often clarifies the right direction immediately.
During testing, observe not only the force needed to deform the part, but also the recovery after a few minutes, any white marks or cracks in the folds, behaviour after repeated cycles and ease of assembly. If the part is intended for an operator, grip, comfort and tactile response must also be considered. If it goes into a machine, load, wear, positioning accuracy and stability over time prevail.
A well-prepared CAD file, accompanied by the function, load conditions and expected quantities, makes it possible to receive a more useful technical comparison than a simple request for "soft TPU". In the move from prototype to small run, this clarity helps maintain repeatability and avoid late changes.
Doppialinea can help check the geometry and production process to turn the functional need into a printed, testable part. The best decision remains the one made on the real component: a sample produced with the intended geometry, orientation and conditions of use provides concrete data on which to set up production with confidence.
