Allbirds: Wool or Tree, and How the Sizing Really Works

Allbirds built its reputation on two things: unusual materials and a shoe simple enough to wear without thinking about it. The materials are the actual decision, and the sizing is where most of the returns come from.

Wool or Tree — this is the choice

Allbirds runs two principal upper materials, and they suit different weather rather than different budgets.

Merino wool is soft, warm and naturally odour-resistant. It regulates temperature well, which means it is comfortable across a wider range than it sounds, but in genuine summer heat it is warm. This is the original Allbirds material and the one most associated with the brand.

Tree is a eucalyptus-based fibre. It is noticeably lighter and cooler, with a smoother, slightly crisper feel. In hot weather it is the clearly better choice.

The practical rule: wool for autumn through spring, Tree for summer and hot climates. If you are buying one pair for year-round wear in a temperate country, wool is the more versatile of the two.

Sizing, and the whole-size problem

Allbirds runs whole sizes only on much of the range, which is fine if you are a whole size and a genuine nuisance if you are not.

The standard guidance is to size down if you are a half size, because the uppers have some give and a loose fit lets the heel lift. The wool styles in particular relax slightly with wear; the Tree styles give less.

Two things worth knowing before ordering. The toe box is roomier than most trainers, so a shoe that feels slightly wide is normal rather than too big. And the shoes are designed to be worn without socks by a lot of people — if you intend to wear socks, factor that in, because it is the difference between sizes for some people.

What they are and are not for

These are comfortable everyday shoes. They are excellent for travel, errands, standing around, and long days that do not involve athletics.

They are not running shoes, whatever the name of a particular model suggests, and the cushioning is not built for repeated impact over distance. They also have limited grip in wet conditions — the smooth soles are a known weak point, and the wool uppers absorb water readily.

If you want one pair for walking a city in mild weather, they are among the best options at the price. If you want one pair for everything, they are not.

Washing them, which is the part people get wrong

Allbirds are machine washable, and this is genuinely one of their better features — but only done correctly.

Remove the insoles and the laces first, wash them separately. Use a gentle cold cycle. Then air dry only. A tumble dryer will shrink wool uppers and the damage is not reversible.

Washing them is also the fix for the odour problem people report. Merino resists odour far better than synthetics, but worn sockless for months without washing, any shoe will give up.

Getting a full life out of them

Wool uppers pill with wear. This is normal for merino and a fabric shaver takes it off in a couple of minutes, restoring the appearance considerably.

The insoles compress before the uppers wear out. Replacement insoles are sold separately and are much cheaper than new shoes — worth knowing when a pair starts feeling flat.

Rotate if you wear them daily. Wool needs to dry out between wears, and that is most of what determines whether they stay fresh.

Which Allbirds model to start with

The Allbirds range looks larger than it is, because the same few shapes come in both materials and a long list of colours.

The Runner is the lace-up everyday trainer and the safest first Allbirds pair. The Lounger is the slip-on version: easier on and off, with less hold at the heel, so the half-size advice above matters more. The Breezer is a warm-weather flat made from the Tree material.

Allbirds has also added more technical models with extra cushioning and grippier outsoles. If you need a shoe for wet pavements or actual running, read the sole description on those rather than assuming an Allbirds Runner will do the job.

Where the Allbirds savings are

Allbirds discounting is modest and fairly consistent, which reflects a brand that rarely runs deep promotions on current stock:

The meaningful savings are in the sale section, where discontinued colourways go at reductions well past any code. Because the core silhouettes — the Runner and the Lounger shapes — change very little year to year, a retired colour is the current shoe at a clearance price.

That is particularly true here because the shoes are deliberately plain. If the colour is the only thing that has been retired, and the colour was never the point, the clearance pair is simply the better buy.

AFF-FIRST15 reads as a first-order offer, so save it for your first Allbirds basket and use the other two on later orders. Codes like these are unlikely to stack with sale prices, so compare the total with and without a code on a clearance pair before deciding.

Common questions

Are they too warm for summer?

The wool ones, for many people, yes. That is exactly what the Tree range is for.

Can I wear them without socks?

Plenty of people do, and merino handles it better than synthetics would. Wash them more often if you do.

How long do they last?

A year or two of regular wear is typical. The soles and insoles give out before the uppers, and neither the soles nor the construction are designed to be repaired.