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A-TPU foam in running shoes

Aliphatic thermoplastic polyurethane — A-TPU — is the foam most often named when people ask whether PEBA has been dethroned. It's the chemistry behind ASICS's FF Leap and Puma's NITRO Elite: springy like PEBA when fresh, but markedly better at holding that spring deep into a shoe's life and across temperatures. Here's what it actually is, why it matters underfoot, and which shoes in our catalog are built on it.

What A-TPU actually is

A-TPU is a thermoplastic polyurethane — the same broad family as the eTPU behind Adidas Boost — but the aliphatic grade. "Aliphatic" refers to the molecular backbone: it's UV-stable, so it resists the yellowing and breakdown that aromatic TPUs suffer in sunlight. Foamed with supercritical gas the way modern super-foams are, A-TPU lands in a sweet spot the older durable TPUs never reached — high energy return and low enough density to be raceable, while keeping TPU's signature resilience and temperature stability.

Brands brand it, as ever, without naming the polymer. ASICS calls its grade FF Leap; Puma calls its grade NITRO Elite. Teardown reviewers — RunRepeat's lab among them — identify FF Leap as aliphatic TPU rather than PEBA, while ASICS itself markets FF Leap as its lightest, softest, and bounciest foam yet. That a brand making both PEBA and A-TPU foams put its A-TPU in a pinnacle racer is a big part of why A-TPU is taken seriously as a PEBA rival rather than a curiosity.

Related: A-TPU is a cousin of the durable TPU behind Adidas Boost (same polymer family, different grade and use case), and a direct rival to PEBA. Most A-TPU midsoles are also supercritically foamed.

Why A-TPU matters for runners

The headline is fatigue resistance. PEBA is lightest and springiest when new, but reviewers widely report PEBA midsoles packing out measurably after 200–300 miles. A-TPU's repeated selling point is that it holds its bounce far longer — both within a single long race and across a season. Believe in the Run made the point bluntly about the Superblast 3's A-TPU: it doesn't lose that bounce after 100 miles. RunRepeat frames the same trait as A-TPU maintaining its energy return where PEBA fades.

The second advantage is temperature stability. Like the broader TPU family, A-TPU changes feel far less in the cold than EVA, and somewhat less than PEBA. RunRepeat's freezer test on the Deviate Nitro Elite 4 measured only about a 6% softness change after 20 minutes frozen — the kind of consistency that matters on a cold start line.

The honest tradeoffs: A-TPU is newer, so the long-term durability picture is still being written, and it's typically a touch firmer and (depending on grade) marginally heavier than the lightest PEBA. For a one-day time trial where every gram counts, the lightest PEBA racers still win the scale. For a foam you'll race repeatedly and train in without watching the bounce die, A-TPU is the stronger case — which is exactly why ASICS often pairs the two in one midsole.

Featured shoes built on A-TPU

ASICS Superblast 3

FF Leap (A-TPU) top + FF Blast Plus (EVA/OBC bio-based blend) base

The shoe that put A-TPU on most runners' radar. The Superblast 3 swapped the previous generation's PEBA top layer (FF Turbo Plus) for FF Leap, a soft A-TPU, over an EVA/OBC carrier. Believe in the Run's verdict captures A-TPU's headline trait: the foam is extra bouncy and, because of its chemistry, doesn't lose that bounce after 100 miles.

ASICS Metaspeed Ray

FF Leap (supercritical A-TPU)

A-TPU as a weight-first racing midsole. The Metaspeed Ray runs a near-full FF Leap midsole in a supercritical grade — ASICS's lightest super-shoe. RunRepeat notes A-TPU's elasticity lets the foam use thinner cell walls that trap less mass, part of how the Ray hits its weight.

ASICS Metaspeed Sky Tokyo

FF Turbo Plus (PEBA) top + FF Leap (A-TPU) base

A-TPU and PEBA in the same shoe. The Sky Tokyo stacks FF Turbo Plus (PEBA) over FF Leap (A-TPU) — ASICS using each foam where it does the most good. A clean illustration that A-TPU isn't a PEBA replacement so much as a complementary super-foam.

Puma Deviate Nitro Elite 4

NITROFOAM Elite (nitrogen-infused A-TPU)

A-TPU as a marathon racer. Puma's NITRO Elite is an aliphatic-TPU compound; the Deviate Nitro Elite 4 runs two layers of it around a carbon PWRPLATE. RunRepeat measured ~77% energy return and only ~6% softness change after the freezer test — the cold-stability A-TPU is known for.

Puma Fast-R Nitro Elite 3

NITROFOAM Elite (aliphatic TPU)

A-TPU at the very top of the racing tier. The Fast-R 3's NITRO Elite is the same aliphatic-TPU compound in Puma's most aggressive racer. The Run Testers describe it as dramatically more durable than ZoomX-based rivals while still hitting marathon-pace energy return.

A-TPU shows up in two shapes: as a full-midsole racing/super-trainer foam (Puma's Fast-R, ASICS's Metaspeed Ray, the Superblast 3), and as one half of a dual-foam racer where it's paired with PEBA (the Metaspeed Sky and Edge Tokyo). For the head-to-head against PEBA, see the FF Leap vs ZoomX page.

Every shoe in the catalog using A-TPU

10 shoes. Includes full-midsole A-TPU and dual-foam constructions where A-TPU is one of the layers.

Sources

Methodology. Chemistry-family detail from polymer references and peer-reviewed work; per-shoe polymer identification from named reviewers and independent teardowns (brands publish foam names and performance, rarely the polymer). Shoe-level commentary is summarized from named reviewers (Doctors of Running, Believe in the Run, The Run Testers, Kofuzi, EDDBUD) — every shoe page linked above carries the original verdicts with source links. Never sponsored, never paid placement.