To wash a sauna hat: hand wash in cool water (20–30°C) with a small amount of wool wash, rinse until the water runs clear, press dry in a towel, reshape and lay flat to air-dry. Merino likes cool water, a gentle wash and a flat dry. Anything else (machine wash, tumble-dry, hot water) will shrink or felt the fibres.
This guide covers the full method for any merino wool sauna hat. It runs through washing, drying and ongoing sauna hat care, with specific notes on the Humi sauna hat — Australian merino, cotton-stitched throughout, and built to take regular washing.
Key Takeaways
- Hand wash in cool water (20–30°C) with wool wash, never machine wash or tumble-dry
- Rinse clear, press dry in a towel, reshape and air-dry flat away from heat and direct sun
- Wash every 8–12 uses; air-dry fully after every session in between
- Persistent smell usually means not enough air-drying, not insufficient washing
- A shrunk hat can partially recover, re-stretch gently over a round form while still damp
How to wash a sauna hat: the six-step method
- Shake out any lint or debris before the hat gets wet.
- Fill a basin with cool water, 20–30°C is the target. Add a small amount of wool wash (roughly a teaspoon is enough).
- Submerge the hat and soak for 10 minutes. Gently press it through the water, no scrubbing, no twisting.
- Rinse in clean cool water until no detergent remains and the water runs clear.
- Press out the water in a dry towel. Roll the towel around the hat and press firmly. Never wring.
- Reshape and lay flat to air-dry away from direct heat and sun. Use the cotton hanging loop inside the crown only once the hat is nearly dry, not while it's still wet and heavy.
What not to do when washing a sauna hat
Never machine-wash, tumble-dry or use hot water to clean a merino sauna hat. The heat and agitation felt the fibres and shrink the hat.
Machine wash. The agitation is the problem, not just the water. Wool fibres have microscopic scales along their length. When those scales are rubbed against each other under heat and friction, as happens in a washing machine, they lock together and compress. This is how felt is made deliberately. Done to a finished sauna hat, it shrinks it permanently.
Hot water. Wool fibres contract when exposed to water above approximately 30°C. A hat that comes out of the wash noticeably smaller is almost always a hot-water problem. Per Woolmark's textile care guidelines, keeping the water cool is the single most important variable.
Tumble drying. Heat accelerates the same contraction. Even a low-heat setting shortens the hat's useful life.
Enzyme and bleach detergents. Standard laundry detergents with enzymes break down keratin, the protein that gives wool its structure. A wool-specific wash, Eucalan, Martha's Wool Wash or any comparable product, is mild enough to clean without damaging the fibre.
Hanging wet. A waterlogged merino hat pulls under its own weight and loses its shape. Lay flat until nearly dry; use the hanging loop after that.
Direct sun. UV exposure weakens wool fibres over time. A cool, ventilated spot out of direct sunlight is the better drying environment.
How often to wash a sauna hat
Wash a merino sauna hat every 8–12 uses, or sooner if it smells or has a visible stain. Between washes, air-dry it fully after every session.
Merino has naturally low-odour properties because of lanolin, a naturally antimicrobial substance in the wool fibre, documented by Australian Wool Innovation. A merino hat used two or three times a week can often go a month between washes and still smell fine. Cotton and synthetic hats need more frequent washing because they lack this property.
The practical rule: dry fully after every session, wash when it needs it. For sizing, shipping and other common questions about Humi, the FAQ covers what isn't in this care guide.
Dealing with sauna hat smell
Most sauna-hat odour resolves with full air-drying, not more washing.
If your hat smells despite regular use, the cause is almost always damp storage. A hat stuffed into a gym bag while still wet will develop odour within a day or two. Give it 12–24 hours to air out fully before putting it away.
For persistent odour, try dry baking soda: sprinkle a small amount inside the hat, leave overnight and brush out in the morning. Skip essential oils, they can stain merino and leave fragrance residue that builds over time.
When to wash rather than air-dry: visible staining, a smell that doesn't resolve after 24 hours of airing, or after an unusually long or high-temperature session.
If your sauna hat shrinks or pills
If it shrinks. While the hat is still damp, gently re-stretch it over a round object roughly the size of your head, a large bowl, a small pot or a tightly rolled towel all work. Stretch gently, leave it to dry fully in that position, and repeat once if needed.
The reason this can work: when a merino hat shrinks in heat, the scale-friction matting that caused it sets while the fibres are wet. Gentle re-stretching while the fibres are still damp and pliable can loosen that set before it dries in. Once the hat has dried in the shrunken shape, recovery becomes harder.
Structural felting, where the hat has hardened and lost all its original texture, is generally not recoverable.
If it pills. Some pilling is normal in new merino, particularly in areas of friction. A fine fabric shaver, or a gentle pull-off with your fingers, handles it cleanly. Pull from the base of the pill, not the tip.
Storing a sauna hat between sessions
Dry it fully first. Always.
Proper sauna hat care between sessions is almost entirely about drying. A hat stored while still damp, even slightly, develops odour faster and is more susceptible to mildew over time.
Humi's sauna hat ships in a 100% cotton storage bag. Cotton breathes, so any remaining trace moisture can escape. Plastic bags and zip-lock pouches trap moisture. If you're keeping the hat in a gym bag, the cotton bag is the right container for it.
For longer storage, weeks between uses, a cool, dry spot with the hat loosely inside its cotton bag keeps it in good condition.
A merino sauna hat washed correctly lasts years of weekly use. The method is simple: cool water, wool wash, flat dry. Avoid heat in every form. Good sauna hat care comes down to that short list. Do those three things and the hat looks after itself.
If you're after a merino hat built to survive regular washing, see the Humi sauna hat — Australian merino, cotton-stitched, with a cotton storage bag included. For other common care questions, see the full FAQ.
Frequently asked questions about washing a sauna hat
Can you wash a sauna hat in the washing machine?
No. Machine washing agitates the wool fibres against each other under heat, causing them to compress and felt, the process that permanently shrinks a hat. Always hand wash in cool water.
Can you put a sauna hat in the dryer?
No. Tumble-dryer heat causes the same fibre contraction as hot water. Remove excess moisture by pressing in a towel, then air-dry flat away from direct heat.
How often should you wash a sauna hat?
Every 8–12 uses for most people, or sooner if it smells or has visible staining. Merino's natural lanolin keeps it low-odour between washes, air-dry fully after every session and you can go longer between washes than you would with cotton.
What detergent should I use to wash a sauna hat?
A wool-specific wash, Eucalan, Martha's Wool Wash or similar. Avoid standard laundry detergents that contain enzymes or bleach; these break down the keratin in wool fibres over time.
My sauna hat shrunk in the wash, can I fix it?
Sometimes. While the hat is still damp, gently re-stretch it over a round object roughly the size of your head. Leave it to dry in that position, and repeat once if needed. Structural felting, where the hat has hardened completely, is generally not reversible.