Athletic footwear marketing is essentially entirely about the midsole, and the material science underneath has moved substantially even where the claims have moved further.
What the midsole does
It sits between the foot and the ground and manages the impact of each step.
Compression absorbs energy. Rebound returns some of it. The balance between them, plus how the foam behaves as it ages, determines the experience.
Every technology in the category is an attempt to improve that trade-off.
The foam generations
Ethylene-vinyl acetate has been the standard midsole material for decades. Cheap, moldable, reasonably durable, and it compresses permanently over time.
Polyurethane is denser and lasts longer, and it is heavier, which is why it fell out of favour as weight became a selling point.
Expanded thermoplastic polyurethane, which appeared in the mid twenty-tens, was a genuine step change — lighter, with substantially higher energy return, and it retains properties in cold better than the alternatives.
Nitrogen-infused and supercritical foaming processes have pushed further, producing lower density at similar performance.
These are real material differences and they are measurable in laboratory testing.
The plate
The other half of the recent change.
Stiff plates embedded in the midsole, usually carbon fibre, alter how the foot flexes and how energy moves through the step.
Combined with thick highly resilient foam, the effect on running economy has been measured in controlled studies and is real, with the effect size varying considerably between individuals.
Governing bodies introduced rules on stack height and plate configuration in competition specifically because the effect was large enough to matter.
Which is about the strongest evidence available that something genuine happened.
What the evidence does not support
The claim that cushioning prevents injury has not held up well.
Studies attempting to link cushioning level or foot type to injury rates have produced inconsistent results across decades.
The motion control category, built on the theory that overpronation caused injury and should be corrected, has weakened considerably as evidence accumulated against the underlying model.
What does appear consistently is that comfort at the point of fitting correlates with lower injury rates, which is a much simpler finding and points toward trying things on rather than toward any category.
Durability
Foam compresses permanently with use, and the point at which it stops functioning is not visible from the outside.
The commonly quoted mileage figures are broad estimates and vary with body weight, surface and gait.
A more reliable signal is the shoe feeling different — flatter, harder, less responsive — which people notice and frequently attribute to themselves rather than to the shoe.
Rotating between two pairs allows foam to recover between uses and extends the life of both, which is well established and rarely mentioned.
The lifestyle category
A large share of athletic footwear is never used for sport, which changes what matters.
For daily walking, midsole technology developed for running is largely irrelevant, and outsole durability and upper construction matter far more.
Which means paying for advanced cushioning in a shoe worn to the shops is paying for a property that will not be used.
What I would actually check
Fit, in the afternoon, with the socks you will wear.
Whether the shoe feels comfortable immediately, since athletic footwear should not require breaking in.
Outsole rubber coverage, since exposed foam on the outsole wears rapidly.
And whether the upper materials will survive — thin engineered knits look modern and tear at the flex points sooner than most people expect.
The upper
Where durability is actually determined for most wearers.
Engineered knit uppers are light and breathable and tear at flex points, particularly where the toe creases.
Layered synthetic uppers with overlays are heavier and hold up considerably longer.
Leather uppers last longest and breathe least.
The toe box and the heel counter are the two areas where structure matters — a collapsed heel counter means the shoe no longer holds the foot, and it is not repairable.
The outsole
Rubber compound and tread pattern determine grip and wear rate.
Harder carbon rubber lasts longer and grips less. Softer blown rubber grips better and wears faster.
Most designs use both, with harder compound at the high-wear areas, and you can see the different colours on the sole.
Exposed midsole foam on the outsole is a weight saving that wears through quickly, and it is visible before purchase.
The environmental question
Athletic footwear is among the hardest categories to recycle, since a shoe combines many materials bonded together.
Separating them is not economically viable at current prices, which is why take-back schemes generally grind shoes into surfacing material.
Mono-material designs and adhesive-free construction have been demonstrated and remain a small fraction of production.
Storage and degradation
Foam and adhesives degrade with time as well as with use.
Polyurethane components hydrolyse in humid conditions, which is why stored footwear can crumble on first wear despite never having been used.
Cool, dry storage slows it and does not stop it, which makes long-term storage of unworn shoes a losing proposition.