The Foam Atlas

Modern running-shoe midsoles are built from a handful of distinct polymer families. Each behaves differently underfoot — different weight, different energy return, different durability, different cost. This atlas explains what the chemistry actually is, why it matters for runners, and which shoes in the Next Pair catalog are built on each foam.

Sources for the chemistry are the manufacturers themselves (Arkema/Pebax, BASF, Dow Chemical) and peer-reviewed work where available. Sources for the shoe-level commentary are named expert reviewers — every claim links back to its origin. We don't fabricate quotes and we don't take brand money.

The foams

• PEBA / Pebax 47 shoes in the catalog Polyether block amide — Arkema's Pebax — is the chemistry behind every modern carbon-plate marathon racer. Lightest-in-class, springiest-in-class, but pricey and not as durable as EVA.
• Supercritical foams 39 shoes in the catalog Supercritical (SCF) foaming and nitrogen infusion turn ordinary EVA, TPEE, or PEBA into lighter, bouncier midsoles by replacing chemical blowing agents with pressurized inert gas. Most modern "super-trainers" sit here.
• EVA 54 shoes in the catalog Ethylene-vinyl acetate. The default running shoe midsole foam for forty years — cheap, durable, predictable, but heavier and less springy than the modern alternatives. Still under the marquee daily trainer in your rotation.
• TPU / eTPU 8 shoes in the catalog Thermoplastic polyurethane — BASF's Infinergy is the famous one (Adidas Boost). Heavy but indestructible. Mostly relegated to durable inserts and stability features now that supercritical EVA and PEBA exist, but the chemistry is having a quiet revival.
• Olefin block copolymers 12 shoes in the catalog Polyolefin elastomers — Dow's Infuse OBC family. Used as a blend partner with EVA (ASICS FF Blast Plus) or as a stand-alone (Nike React, On Helion). Energy return between EVA and TPU; durability profile genuinely good.

How to read these pages

Each foam page covers four things: (1) the chemistry — what the polymer actually is and how the foam is processed; (2) the runner tradeoffs — weight, energy return, durability, ride feel; (3) a handful of featured shoes that are good representatives of the foam, each with a one-line case for picking it; and (4) the complete catalog appendix — every approved shoe in our database that uses that chemistry, linked.

A single shoe often appears on more than one page. Modern racers routinely stack a PEBA top layer over an EVA carrier, and a "supercritical" foam might be supercritical EVA, supercritical PEBA, or supercritical TPEE. Where that happens we list the shoe on every applicable page so the appendix really is exhaustive.