Sauna hats look like a joke to anyone who has not used one and are standard equipment to anyone who has. The reason is physical rather than cultural: your head sits in the hottest layer of the room and has the least tolerance for it, so insulating it lets the rest of you stay in longer.
Why they work
Heat stratifies, so the air at head height on an upper bench is markedly hotter than at your chest. A thick wool or felt hat traps a layer of cooler air against your scalp and slows that heat reaching you. The practical result is that the session stops being limited by your head feeling unbearable before the rest of you has warmed through.
Wool, felt and linen
Merino and sheep wool felt are the traditional choice because wool insulates while still breathing and handles repeated wetting. Linen is cooler, lighter and better in an already mild cabin or a steam room, where felt gets heavy and sodden. Avoid anything synthetic: it holds no useful air, traps sweat and can soften at cabin temperatures.
Fit and care
A hat wants to cover the crown and the tops of the ears without gripping, because a tight band on a hot head is uncomfortable within minutes. Felt shrinks if you wash it warm, so rinse cool and dry flat away from the stove. Most owners keep two so one is always dry, which matters more than the price of either.
Do you need one
In an infrared cabin, no: the air stays cool and there is no hot layer to sit in. In a traditional sauna run above about 180, most regular users find one makes a real difference, and in a hot public sauna they are close to universal. It is the cheapest accessory that changes how long you can comfortably stay.
Questions people ask about sauna hats
Do sauna hats actually do anything?
Yes. They insulate your head from the hottest layer of air in the room, which is usually what ends a session before the rest of you is ready.
Wool or linen?
Wool felt for a hot traditional sauna, linen for a cooler cabin or a steam room where felt becomes heavy and waterlogged.
Can you wear one in an infrared sauna?
You can, but there is little point. Infrared warms your body directly and the air stays cool, so there is no hot layer to shield from.