Supercritical foams in running shoes

Supercritical foaming — and its cousin, nitrogen infusion — is a processing technique, not a polymer family. It turns ordinary EVA, PEBA, or TPU into a lighter, bouncier midsole by replacing chemical blowing agents with pressurized inert gas. Almost every modern "super-trainer" sits here. Here's what's actually going on chemically and which shoes in our catalog use it.

What "supercritical" actually means

"Supercritical" refers to a state of matter — a fluid above its critical temperature and pressure where the distinction between liquid and gas dissolves. Supercritical CO₂ and supercritical nitrogen flow like a gas (so they penetrate everywhere) but dissolve solutes like a liquid (so they actually expand the polymer matrix). When the pressure is released, the gas rapidly comes out of solution, foaming the polymer from the inside out.

The conventional way to foam a midsole is to mix the polymer pellets with a chemical blowing agent — typically azodicarbonamide — and a cross-linking peroxide, then heat-press the mix in a mold. The blowing agent decomposes and releases gas, which expands the foam. The resulting cell structure is functional but uneven, with relatively large cells and material trapped between them.

Supercritical foaming replaces the chemical blowing agent with pressurized supercritical CO₂ or N₂ that dissolves into the polymer melt. When the pressure drops, the gas comes out of solution everywhere at once, producing very small, very uniform cells throughout the polymer. The downstream property profile is measurably different: lower density (the foam holds more gas per unit polymer), higher rebound, and — depending on the polymer family — a more "lively" feel underfoot. BASF developed the technique commercially for footwear in the 2010s with their Infinergy / Boost program; almost every brand has its own variant today.

"Nitrogen-infused" is a closely related — but not identical — process. Brands including Brooks (DNA Loft v3, DNA Tuned) and Mizuno (Enerzy NXT) inject nitrogen gas during foaming without necessarily reaching the full supercritical regime. The result is similar — finer cells, bouncier ride, lighter weight — but the process control is different and the property profile sits between conventional and full supercritical.

Related: The base polymer matters as much as the processing. EVA, PEBA, TPU, and olefin blends all show up in supercritical form. The chemistry sets the ceiling; supercritical processing helps the foam reach it.

Why supercritical matters for runners

The honest answer is that "supercritical" by itself is not the feature — the property profile of the resulting foam is. A well-formulated conventional EVA can outperform a poorly formulated supercritical EVA. What supercritical processing does reliably is: lower the density of the foam, increase the rebound resilience, and produce a more uniform cell structure that feels more consistent across the foot strike.

The Run Testers and Doctors of Running both treat the Novablast 5 → Megablast comparison as one of the cleanest A/B tests in the catalog: same base polymer (FF Blast Max, an EVA / OBC blend), different processing (conventional vs supercritical), measurably different ride. The Megablast is bouncier, slightly lighter, and noticeably more "alive" at conversational pace. That difference is what the supercritical step buys you.

The honest tradeoffs: supercritical processing is more expensive (specialized pressurized equipment, slower cycle times). The durability of supercritical foams is generally somewhere between conventional EVA and pure PEBA — better than PEBA, worse than plain EVA. And the property gain is most pronounced for foams that were already energetic — supercritical PEBA is the foam that's measurably set marathon world records (Adidas Adizero Adios Pro Evo). The gain on commodity foams is real but smaller.

For runners, the practical read is: supercritical is reliable shorthand for "this foam is among the bouncier examples of its polymer family." It is not a guarantee of bounce — chemistry matters more — but in 2026 the "super-trainer" daily shoes that feel meaningfully springier than their predecessors almost all use this processing step.

Featured supercritical shoes

ASICS Megablast

FF BLAST MAX (supercritical EVA)

FF Blast Max in supercritical form — same EVA / OBC blend as the Novablast, but blown with pressurized inert gas instead of a chemical blowing agent. The Run Testers describes the difference as a real step-change in liveliness, not marketing. The Megablast became a marquee 2026 daily trainer because of this processing change, not a polymer change.

HOKA Bondi 9

Supercritical EVA

Supercritical EVA in a max-cushion context. Hoka swapped the previous-gen Bondi's compression-molded EVA for a supercritical formulation; Believe in the Run notes the new Bondi is meaningfully bouncier than the Bondi 8 even at the same stack height. Same chemistry family, different processing, different ride.

Adidas Adizero Adios Pro Evo 2

Lightstrike Pro Evo (supercritical TPEE)

Supercritical TPEE — Adidas' Lightstrike Pro Evo (teardowns identify Lightstrike Pro as a TPEE, not PEBA). Effectively the lightest and bounciest racing midsole on the market, and the reason the original Pro Evo set the marathon world record. EDDBUD describes it as the closest a foam has gotten to feeling like a literal spring underfoot.

Saucony Ride 19

PWRRUN+ (supercritical eTPU)

Supercritical TPU. Saucony's PWRRUN+ in the new Ride is supercritical eTPU — same chemistry family as Adidas Boost, but processed differently. The Run Testers notes the new Ride keeps the durability the Ride line has always had and adds back the bounce TPU is famous for.

Brooks Glycerin Max 2

DNA TUNED (nitrogen-infused EVA, dual-size cells)

Nitrogen-infused EVA. Brooks' DNA Tuned uses dual-size cells from a nitrogen-foaming process — not full supercritical, but in the same family of inert-gas-foamed midsoles. Doctors of Running uses the Glycerin Max as a reference for max-cushion daily training; the foam does most of the work the rocker doesn't.

Each of these uses a different base polymer with the same processing family — supercritical EVA (Megablast, Bondi 9), supercritical PEBA (Pro Evo 2), supercritical TPU (Ride 19), and nitrogen-infused EVA (Glycerin Max 2). It's the clearest way to see what the processing step actually contributes versus the chemistry.

Every supercritical / nitrogen-infused shoe in the catalog

66 shoes. Includes supercritical EVA, supercritical PEBA, supercritical TPU/TPEE, and nitrogen-infused variants where one of the layers uses inert-gas foaming.

Sources

BASF — Infinergy expanded TPU (manufacturer page on the original commercial supercritical-foamed footwear polymer; basis for Adidas Boost).
Di Maio & Kiran — Foaming of polymers with supercritical fluids and perspectives on the current knowledge gaps and challenges, Journal of Supercritical Fluids, 2018 (peer-reviewed review of supercritical polymer foaming).
Yang et al. — Super-Elastic and Dimensionally Stable Polyether Block Amide Foams Fabricated by Microcellular Foaming with CO2 & N2 as Co-Blowing Agents, Macromolecular Materials and Engineering, 2024 (peer-reviewed; how CO2/N2 co-blowing-agent microcellular foaming yields super-elastic, dimensionally stable PEBA foam).
RunRepeat — The ultimate guide to running shoe foams (independent lab measurements comparing conventional vs supercritical foams on energy return and softness).

Methodology. Chemistry sourced from manufacturer technical data and peer-reviewed work. 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.