Wool vs Felt Sauna Hats: Boiled Wool, Felt, Cotton and Linen

Boiled wool and felt are made of the same fiber and rely on the same trick: wool locks together under heat, moisture and friction. The difference is the starting point. Felt is built up from loose fibers, while boiled wool starts as a finished fabric that is then shrunk by 10 to 25 percent, according to Britannica. Here is how those two compare with cotton terry and linen when the room hits 176°F (80°C) and someone throws water on the rocks.

Key takeaways

1. Boiled wool starts as fabric and is shrunk until dense.
2. Pressed felt is built from loose fibers.
3. Cotton terry is soft, absorbent and easy to wash.
4. Linen is light and dries quickly.
5. Heat and steam affect each material differently.
6. Choose by how you sauna, not by what is trendy.

1. Boiled wool starts as fabric and is shrunk until dense

Boiled wool, called Wollwalk in German, begins as a regular wool fabric. It is then fulled: Britannica describes fulling as exposing woven or knitted wool to moisture, heat, friction and pressure until it shrinks by 10 to 25 percent. The result is what Britannica calls a smooth, tightly finished fabric that is light, warm and relatively weatherproof. Austrian loden cloth, first made in the 16th century, is a classic example. For a sauna hat, boiled wool has a few practical traits:

• It is dense but still flexible, so it can be folded and adapts to different head shapes.
• It packs flat in a bag.
• Thickness can be adjusted by layering. Our Original is a single layer, the Pro is a double layer that keeps its shape on its own.

The trade off: a single layer is thinner than a thick felt hat, so it insulates a little less on its own.

2. Pressed felt is built from loose fibers

Felt skips the fabric stage. Britannica defines felting as the consolidation of fibrous materials by heat, moisture and mechanical action, and names wool, fur and certain hair fibers as the materials that felt, thanks to their structure and crimp. Many felt sauna hats are made of wool felt and shaped into a cone or a bell with a brim. In the Russian banya they are a familiar sight. The Moscow Times describes bathers putting on felt hats before they start, meant to protect them from the extreme heat. What felt does well:

• It can be made thick, which gives a lot of insulation.
• It holds a sculpted shape and looks unmistakably like sauna gear.

The trade off: thick felt tends to be stiffer and slower to dry, and a molded shape does not adapt much to your head, so size matters more.

3. Cotton terry is soft, absorbent and easy to wash

Terry is the looped fabric of bath towels. Merriam-Webster defines terry cloth as an absorbent fabric with uncut loops, and that is its strength. Terry turbans and cotton caps are soft, cheap and go straight into the washing machine. They are a sensible option for anyone who wants a covering that is easy to keep clean. In heat and steam, cotton behaves differently from wool. It holds less moisture from the air: the ASTM D1909 standard table lists a commercial moisture regain of 13.6 percent for wool, against 7 to 8.5 percent for cotton yarn. In a sweaty round, cotton soaks up liquid readily and then simply feels wet and heavier on your head. Cotton also ignites at a much lower temperature than wool, 491°F (255°C) versus 1,058 to 1,112°F (570 to 600°C), according to the Woolmark Company. That matters only if a hat ends up on the heater, which it never should.

4. Linen is light and dries quickly

Linen is made from flax, and it has fans in Nordic saunas. The Helsinki city guide MyHelsinki suggests bringing a reusable linen seat cover for the benches, and some people like linen on their heads too. Britannica notes that linen is stronger than cotton, dries more quickly and is more slowly affected by sunlight. Its low elasticity makes it wrinkle, which hardly matters for a sauna cap. In the ASTM table, linen sits at 8.75 percent moisture regain, closer to cotton than to wool. In practice, a linen cap is thin and airy. It shades your head from the hottest air rather than wrapping it in a thick insulating layer. That makes it pleasant for milder saunas or for people who find wool too warm, and less of a buffer during strong steam rounds on the top bench.

5. Heat and steam affect each material differently

Here is a fair summary of how the four behave in a hot cabin:

• Boiled wool: dense, moderate thickness, flexible fit. Wool can absorb up to 35 percent of its weight in moisture before it feels wet, according to Woolmark.
• Pressed felt: same fiber, often thicker and more rigid. Strong insulation, slower to dry.
• Cotton terry: absorbs liquid quickly, then feels wet and heavy. Very easy to wash.
• Linen: thin and airy, dries fast, offers less insulation.

Both wool versions need the same care: no hot water and no hard rubbing, because the fibers can keep felting. Our guide on how to wash a wool sauna hat explains why. Cotton and linen are more forgiving in the laundry. Whatever you choose, never dry any hat on the heater.

6. Choose by how you sauna, not by what is trendy

There is no single right material. A few honest pointers:

• You love strong steam rounds on the top bench: wool, either thick felt or a double layer of boiled wool like the Pro.
• You want one hat that fits well, folds flat and travels easily: boiled wool, like the Original in Basalt or one of its five other colors.
• You like the classic banya look and do not mind a stiffer shape: felt.
• You mostly visit mild saunas and want machine washable: cotton or linen.

We chose boiled wool because it adapts to the head instead of the other way around. Our founder's first hat, which he sewed for himself because his head got too hot, was the starting point.

FAQ

Is felt the same as wool?

Not exactly. Wool is the fiber, felt is a way of turning fibers into a material. Most felt sauna hats are made of wool felt, while boiled wool is wool fabric that was shrunk until dense.

Which is better for a sauna hat, wool or felt?

Both are wool, so they handle heat in a similar way. Felt hats tend to be thicker and more rigid, boiled wool hats are more flexible and adapt to your head.

Can I wear a cotton beanie in the sauna?

You can, especially in a milder sauna. Expect it to get damp and heavy with sweat, and skip hats with metal parts such as rivets or pins, since metal gets hot.

Compare colors and sizes in our sauna hat collection. Wondering whether a towel would do the job just as well? Read Sauna hat vs towel.