The new PEBA foams last longer than EVA. I’ve done benchtop materials testing on new VaporFly Next% and ones with 500 km (300+ miles) and the compliance (softness) and resilience (energy return) were very very close to the original values. The energy return dropped from ~85% to ~83%, still dramatically higher than old foams. The compliance was also nearly identical.
For this reason, among others, I’ve switched to doing a lot of my own training in super shoes. The integrity of the shoes seems more predictable, especially as these new polymers are more robust to temperature changes.
The life-limiter on the shoes actually seems to be the physical integrity of the foam, where the abrasion from the road rips it up (unevenly for most people, ie, on the lateral or medial portions), as most have only minimal rubber on the bottom for weight. I typically send my super shoes to the graveyard when the foam gets ripped up enough to feel like the shoe isn’t level anymore on the ground.
We wrote about this in a paper that was just published (pg. 3, “AFT Foam Durability”). It’s still open access, so feel free to check it out: