We've been in the sauna industry for a while now and see the same misconceptions about sauna hats come up constantly, so figured we'd write this out.
They're not about keeping your hair dry. The whole point of a sauna hat is head, hair, and brain protection. Your head is the most heat-sensitive part of your body - blood vessels there are close to the surface and your brain reacts quickly to temperature spikes. A proper sauna hat insulates your head so you can stay in longer without it overheating before the rest of your body is ready to leave.
Material matters more than most people think. Thick-felted wool is the traditional choice. It breathes, insulates without cooking you, and holds up in high humidity. Mesh hats serve a different purpose: airflow and comfort during longer, lower-heat sessions. Neither is wrong - it comes down to your sauna temperature and how long you like to sit.
Why Finnish sauna culture developed them: Traditional Finnish saunas run 176–212°F. At those temperatures, head protection isn't optional if you want a proper session. The hat lets you stay seated at bench level without cutting things short because your head gives out first. There are 3.3 million saunas in Finland for 5.5 million people — they've had a long time to figure this out.
Do you use one? What's been your experience?