Buy on density first. A sauna hat works because the felt between your head and the air is thick enough to insulate — everything else is secondary. Most hats sold as sauna hats fail that one test, which is why so many people try one and conclude it doesn't do much.

Here is what matters, in order.

1. Thickness and density

This is the whole game. Dense wool felt is a poor conductor of heat, so it slows the transfer of hot air to your scalp. Thin felt doesn't — and worse, once it saturates with sweat and steam it starts conducting heat rather than resisting it. That happens at exactly the point you need it most.

Look for felt measured in millimetres, not described in adjectives. Ours is hand-felted to roughly 6mm, three to six times thicker than the thin pressed hats sold alongside it. You can feel the difference holding both.

If a listing won't tell you a thickness, assume there's a reason.

2. Seamless construction, not good stitching

The usual advice is to check the stitching. We'd put it the other way round: the fewer seams, the better. Seams are where heat, moisture and repeated wear do their work, and a hat cut from thin sheet felt and sewn together carries a seam straight through the area meant to be protecting you.

Hand-felting produces a single unified structure with no seams to fail. It insulates evenly, holds its own shape, and there's nothing to come apart. It's the difference between a hat that's been manufactured and one that's been made.

3. Wool — and nothing but wool

Wool has been the material for this for centuries, for good reasons. It insulates, it manages moisture, it keeps working when damp, and it's naturally antimicrobial, so it resists odour through repeated use.

• 100% wool felt — what you want. Breed matters far less than density; a thick, honestly made felt beats a thin one with a better-sounding name on it.
• Cotton or linen — breathable, but they offer very little heat protection above 80°C. Fine for a steam room, not for a hot sauna.
• Synthetics — avoid entirely. Polyester and nylon trap heat against the skin, hold odour, and degrade in humidity. Nothing synthetic belongs in a 90°C room.

4. Fit should mould, not adjust

Ignore straps, drawstrings and adjustable sizing — they're solving the wrong problem. A dense wool hat should sit close without gripping, and then improve: heat and wear gradually mould the felt to the shape of your head, so it fits better at session fifty than at session one.

What to check instead:

• It covers your ears. Ears take the heat badly and are the first thing people notice going wrong.
• It stays put when you lean back against the bench.
• It holds its own shape rather than collapsing onto your scalp.

On shape, be sceptical of the claim that taller is automatically better. The traditional cone is traditional, not magic — height alone insulates nothing. Density and coverage do the work.

5. Whether it will survive being used

Sauna conditions are punishing: high heat, steam, and use several times a week. Before you buy, ask whether the hat can be cleaned without being wrecked, and whether it will still be the same shape in a year.

A good wool hat is spot-cleaned and air-dried, never soaked or machine washed — saturating wool felt distorts it permanently. If a hat needs regular washing to stay usable, the wool isn't doing its job. Full detail in our care guide.

What to ignore

Colour, branding and novelty shapes tell you nothing about performance. Neither does price on its own — though felt of genuine thickness costs more to make, so a very cheap hat is usually cheap for a structural reason.

The short version

Density, then construction, then material, then fit. Get the first one right and the hat will do what you bought it for: keep your head cooler than the room, protect your hair from the heat, and let you stay in longer.

More on why the thin ones fail: why most sauna hats don't work. Or see our handcrafted wool sauna hats — free shipping on 2+ items.

Built for heat. Made to last.