What ETPU is
ETPU starts as solid TPU pellets. Each pellet is expanded with gas into a closed-cell bead roughly the size of a lentil. Thousands of these beads are then fused together into one part. The result is a foam with two levels of structure: fine cells inside each bead, and the beads themselves acting as small springs.
How ETPU midsoles are made
- Impregnation — TPU pellets are saturated with a gas, typically carbon dioxide or nitrogen, under pressure.
- Expansion — A sudden pressure drop or heat makes the gas expand, puffing each pellet into a lightweight bead.
- Steam-chest molding — Beads are filled into a mold and fused with pressurised steam, which welds their surfaces together.
- Stabilising — Parts are cooled and conditioned so they hold dimensions before assembly.
No chemical blowing agent or cross-linker is used, which keeps the material a thermoplastic. Newer processes fuse beads with radio-frequency energy instead of steam, using less energy and water.
Cushioning: 6 / 8, High
ETPU cushions well, but its feel is bouncy rather than sink-in soft. The beads compress and spring back quickly, so the foot feels supported and propelled rather than absorbed. Bead size, bead density and fusion pressure set how firm the midsole feels.
Rebound: 8 / 8, Max
Rebound is ETPU's signature. The elastic TPU in each bead returns most of the energy put into it, and that response stays consistent from cold to warm conditions. In ball rebound testing such as ISO 8307, ETPU sits well above EVA and PU.
Durability: 8 / 8, Max
ETPU resists compression set much better than EVA. The beads recover their shape after load, so the midsole keeps its height and feel over a long service life. The trade-off is weight: ETPU is denser than EVA and the newest PEBA-based foams, which is why many racing shoes have moved on, while ETPU remains strong in daily trainers and lifestyle footwear.
Where ETPU is used
- Daily running trainers — durable, springy cushioning for high weekly mileage.
- Premium lifestyle sneakers — the visible bead texture has become a design feature in itself.
- Comfort-performance hybrids — walking and work shoes that need lasting comfort with some energy return.
- Insoles and inserts — ETPU footbeds and heel pads add rebound to existing shoes.
Designing with ETPU
Choose ETPU when the shoe should feel springy and keep that feel for a long time.
- Choose PEBA-based foam when the lowest possible weight matters more than longevity and cost.
- Contain ETPU with a frame or carrier; on its own it can feel unstable at high stack heights.
- Use a rubber outsole over the beads; exposed ETPU can tear and pick up debris.
- Plan for weight — a full ETPU midsole is heavier than the same volume of EVA.
- Consider TPU-compatible components to keep the sole closer to a single material family.
