A gasket that takes a permanent dent stops sealing. A cushion that flattens stops cushioning. A snap that relaxes stops holding. For a whole class of parts, the property that matters is not how they perform on day one but how well they keep recovering their shape under sustained load. For TPU, that comes down to two related ideas: compression set and resilience.
This guide explains both, with grade data, and shows how temperature quietly governs the result. For where this property sits in the full selection picture, see the TPU material selection guide.
Editorial note: This is an independent educational guide. Values are illustrative of published TPU grades and standard tests, not a specification. Always compare grades at the temperature and conditions of your application and verify with testing.
The question: will the part spring back?
Strip away the jargon and the design question is simple: after this part is squeezed, held, and released, does it return to its original shape, or does it stay deformed? For seals, gaskets, cushions, vibration mounts, and snap features, the answer determines whether the part still does its job months or years in. A material can be strong, tough, and abrasion-resistant and still fail here if it takes a permanent set under load.
Compression set, creep, and resilience
Three terms get tangled together. Keeping them straight is half the battle:
- Compression set — permanent deformation left after the material is held at a constant strain (squeezed by a fixed amount) and then released. Reported as a percentage; lower is better recovery.
- Creep — ongoing deformation under a constant stress (a fixed load that stays applied). The part keeps slowly deforming over time under that load.
- Resilience — how efficiently the material returns deformation energy: how much it springs back versus how much it absorbs.
The distinction that trips people up is set versus creep. Compression set is constant strain; creep is constant stress. A gasket squeezed to a fixed gap is a compression-set problem; a clip holding a steady load is a creep problem. They are measured differently and you should ask for the one that matches how your part is loaded.
How compression set is measured
A standard compression-set test squeezes a specimen to a set deflection, holds it at a defined temperature for a defined time, releases it, lets it recover, and measures how much thickness did not come back. The result is a percentage — 0% would be perfect recovery, 100% would be no recovery at all.
Two details make or break the comparison: temperature and time. A compression-set number is meaningless without them. "25% compression set" at room temperature for three days is a very different statement from the same number at 100 °C, and comparing grades tested under different conditions tells you nothing.
Temperature is the killer
Compression set climbs with temperature, and the climb can be steep. The same grade that recovers well in a cool environment can take a much larger permanent set when it is held compressed while hot. This is the single most common reason a seal that passed a bench test fails in service: it was specified on a room-temperature number and then asked to work warm.
The discipline is straightforward — match the test temperature to the application. If the part will be hot under load, the compression-set value that matters is the hot one, full stop.
Compression set across grades and temperatures
Published TPU grades show both the temperature effect and the difference between grades. Note how the same grade gets worse as temperature rises:
| Grade | 23 °C / 72 h | 70 °C / 24 h | 100 °C / 24 h |
|---|---|---|---|
| Soft aliphatic polyester TPU (~68 Shore A) | ~25% | ~35% | ~50% |
| Rigid polyether TPU (~43 Shore D) | ~30% | ~45% | — |
Follow the first row across: compression set roughly doubles from 25% at room temperature to 50% at 100 °C. The material did not change — the temperature did. That is the whole argument for testing at the application temperature in one line.
Resilience, rebound, and damping
Recovery is not only about avoiding permanent set; it is also about how the material returns energy in the moment. TPU is unusual among elastomers in offering both strong rebound and strong damping. Rebound returns energy — useful for energy-return cushioning and springy parts. Damping absorbs energy — useful for shock absorption and vibration control. Different TPU grades lean one way or the other, so the same family can serve a bouncy wheel and a vibration mount.
There is also a quiet link to hardness testing here. In a durometer reading, a more resilient, higher-strength material creeps less under the indenter than a weak one, so a delayed hardness reading reflects resilience as well as hardness. It is a small reminder that recovery behavior shows up across multiple measurements — see understanding Shore hardness for that connection.
When TPU is, and is not, a sealing material
Compression set is where you have to be honest about TPU's limits. For demanding long-term static seals — gaskets that must hold a sealing force for years, especially when warm — thermoset rubber and TPV often recover better and are the more natural choice. TPU's compression-set values, particularly at elevated temperature, are moderate rather than best-in-class.
Where TPU earns the sealing job is when sealing comes bundled with abrasion, tear, or impact duty — a dynamic seal that also takes wear, or a sealing part that must survive rough handling. There, TPU's toughness can outweigh a rubber's better pure-recovery numbers. The honest selection rule: if the part is purely a static seal, look hard at rubber or TPV; if it seals and takes abuse, TPU comes back into contention. This mirrors the broader trade-off in TPE vs silicone vs thermoset rubber.
How to specify recovery properly
To get a part that actually springs back, put the right things in the spec:
- State whether the part is loaded at constant strain (use compression set) or constant stress (use creep).
- Give the service temperature and require compression-set data at that temperature.
- Give the duration of the load — short clamp or years of squeeze.
- Note whether rebound or damping is the goal, if recovery energy matters.
- For seals, ask whether rubber or TPV would recover better before defaulting to TPU.
- Confirm with testing under the real load, temperature, and time.
Bottom line
Whether a TPU part keeps springing back is governed by compression set, creep, and resilience — and by temperature most of all. Compression set is constant-strain recovery, creep is constant-stress deformation, and both get worse as the part runs hotter; published grades can roughly double their compression set from room temperature to 100 °C. TPU brings a rare mix of rebound and damping, which suits cushioning and energy-return parts, but for pure long-term static sealing, rubber or TPV often recovers better. Specify the right test, at the right temperature, for the right duration — and verify it.
For clear definitions of compression set, creep, and service temperature, the Avient thermoplastic elastomer FAQs are a useful reference.
FAQ
What is compression set in TPU?
Compression set is the amount of permanent deformation left after a material has been held compressed and then released. It is reported as a percentage: a lower value means the part recovered more of its original thickness, which matters for seals, gaskets, and any part that must keep pushing back over time.
What is the difference between compression set and creep?
Compression set is deformation under a constant strain — the part is squeezed to a fixed amount. Creep is deformation under a constant stress — a fixed load is applied and the part keeps deforming over time. Seals are usually a compression-set problem; load-bearing parts are usually a creep problem.
Does temperature affect compression set?
Strongly. Compression set rises with temperature. A grade that recovers well at room temperature can show much higher set when held compressed at elevated temperature, so the test temperature must match the application.
Is TPU good for seals and gaskets?
TPU can be used for sealing, but for demanding long-term static seals where low compression set is critical, thermoset rubber or TPV often performs better. TPU is a stronger choice where abrasion, tear, or impact accompany the sealing duty.
What is resilience in an elastomer?
Resilience is how efficiently a material returns the energy used to deform it — how much it springs back versus how much it absorbs. TPU is unusual in offering both strong rebound and strong damping, which is why it suits both energy-return and shock-absorbing parts depending on the grade.
How can I tell if a TPU will recover well?
Look at the compression-set values on the data sheet, and crucially at the temperature and time of the test. Compare grades at the temperature your part will actually see, not just the room-temperature number, and confirm with testing under real conditions.
Related: TPU Material Selection Guide → · TPE vs Silicone vs Thermoset Rubber →