Nike React and Air: what each one actually does
Two different things travel under one heading. React is a foam and runs the length of the sole. Air is a sealed unit of pressurised gas and sits at one point, usually under the heel. They are not versions of each other, and the one you can see through the window is rarely the one doing the work.
Two things, one name
React is a foam, and like every foam it works by being compressed and springing back along its whole length. Air is a pocket of gas sealed in a tough plastic skin: it is pressed flat at the point where it sits and pushes back from there. A shoe can carry one, the other, or both – and most Nike running shoes now carry both.
The window in the sole
The visible bubble is the most recognisable thing Nike has ever done to a shoe, and it is worth being clear about what it tells you. It was an act of design, not of engineering: the technology had existed for nine years before anyone cut a hole to show it. Making it visible is what sold it.
On a running shoe, a large visible unit under the heel does cushion the heel. On a lifestyle shoe it is mostly there because it is the shape people recognise. Neither is dishonest, but the size of the window is not a measure of how much cushioning you get, and it says nothing at all about what the rest of the sole is made of – which, on a running shoe, is where most of the ride comes from.
The plainest way to read a spec sheet: Air tells you what is at one point of the sole. Foam tells you what the sole is.
The versions
Both names have been through several generations, and the differences are real rather than cosmetic:
- Air – the original sealed unit, from 1978. The idea came from an aerospace engineer, Frank Rudy, and the first shoe to carry it was the Tailwind.
- Air Max – from 1987, the version with the window. Bigger volume, softer landing, and the one most people picture.
- Zoom Air – a flatter unit with tensioned fibres strung inside it. It compresses less and returns faster, which is why it turns up in racing and tempo shoes rather than in cushioned trainers.
- React – the foam, from 2017, built to be soft and springy at once and to hold that for longer than the foams before it.
- ReactX – the 2023 replacement. Nike states more energy return and a considerably smaller carbon footprint in the making.
ZoomX is not Air
Despite the name, ZoomX contains no air unit at all. It is a foam – the very light, very springy kind used in racing shoes – and it has nothing in common with Zoom Air but the word.
If you are comparing two shoes and one lists Zoom Air while the other lists ZoomX, you are comparing a gas unit with a foam.
Which one you actually want
For everyday running miles, the foam is what you will feel. React or ReactX under the whole foot gives an even ride that does not change much from the first mile to the last, and a heel unit on top of it mostly smooths out the landing. This is the combination in most of Nike’s daily trainers, and it is the safe answer if you want one pair.
For faster running, the logic reverses. A shoe that sinks is a shoe that gives energy back late, so tempo and racing models use firmer, faster-returning parts – a flat Zoom Air unit, or a springy foam with a plate – and accept less comfort for it.
For walking and for standing about, a big visible unit is genuinely comfortable and that is a fair reason to buy one. It is just not a running argument.
How the two age
They fail in opposite ways, and this is the part no shop mentions.
Foam packs down. It loses its spring gradually, over hundreds of miles, and because the change is slow you adapt to it without noticing. The shoe that feels fine is often a shoe you have simply got used to. React was designed to slow this down and does, but it does not stop it.
A gas unit does not pack down at all – until the skin is punctured or a seam fails, and then it goes at once. A flat unit does not come back. This is rare, and much rarer than foam wearing out, but it is a different kind of ending: gradual on one side, sudden on the other.
Which matters for how you judge a worn pair. With foam, trust the mileage rather than the feel. With an air unit, look at it.
Where you’ll find it
Shoes on this site built around React or Air. They are examples of what the technology does in practice, not a catalogue.
See it in the full table, where you can filter by activity, material and price.
Similar and competing technologies
Every brand solves the same problem – take the impact, give something back, stay light – and the answers fall into a few families rather than into a long list of names.
| Family | How it works | What it trades |
|---|---|---|
| Standard foam · React, Fresh Foam, DNA Loft | Compressed and springs back along the whole length of the sole. | Durable and predictable, but heavier than the newer foams and it packs down in the end. |
| Blown foam · Boost, NITRO, PWRRUN | Gas forced into the material under pressure, or fused beads of it. | Lighter and livelier for the weight; the trade is usually cost, and sometimes how it behaves in the cold. |
| Supercritical foam · ZoomX, PWRRUN PB | A different base plastic, foamed under pressure. Very light, very high return. | Expensive, and it wears out faster. Racing shoes are not built to last. |
| Sealed gas unit · Air, Air Max, Zoom Air | A pocket of pressurised gas at one point of the sole. | Does not pack down, but cushions where it sits and nowhere else – and fails all at once if it is punctured. |
The midsole is where nearly all of this happens, and a plate – carbon or otherwise – is a separate question laid on top of whichever foam a shoe uses.