Sauna Hat Size Guide: How to Measure and Pick Your Fit

Wrap a tape measure around your head just above your ears and eyebrows, read the number in centimetres, and that's your hat size. Under 60cm, take a Halo in M. 60cm or more, take XL. If you're right on the line, take M, because wool felt relaxes slightly with wear. That's the whole guide. The rest is detail for the edge cases.

Why sauna hat sizing matters more than you'd think

Most sauna hats are one size. The brands selling them will tell you one size fits most, and for the middle of the range that's true. It's not true for the roughly one in five people whose heads sit outside the middle [1].

A hat that's too tight grips your temples and you'll take it off before the round ends. A hat that's too loose slides over your eyes when you lean forward, and the brim lets hot air in around the sides, which is exactly where the insulation needs to seal. Either way the hat isn't doing its job. Fit isn't comfort. Fit is function.

How to measure

You need a soft tape measure, or a piece of string and a ruler.

1. Wrap the tape around your head at the widest point: across the forehead about 1cm above the eyebrows, above the ears, and around the fullest part at the back.
2. Keep the tape snug but not tight. It should sit flat against your skin, not dig in.
3. Read the measurement in centimetres.
4. Measure twice. If the two readings differ, use the larger.

If you use string, mark where it overlaps and lay it flat against a ruler.

Measure with your hair as you'd wear it in the sauna. If you tie long hair up under the hat, measure with it up.

Halo sizing

Both sizes are the same 7mm dual-layer Australian wool felt and the same shape. The only difference is the circumference.

For reference, average adult head circumference in large anthropometric surveys is around 55 to 57cm for women and 57 to 59cm for men, with the full adult range running from about 52cm to 64cm [1, 2]. M covers the bulk of that range. XL covers the top.

Long or thick hair

Hair takes up room. A lot of thick or curly hair, or long hair worn up under the hat, can add 1 to 2cm to your effective measurement.

If you measured with your hair down and it's long or thick, and you came in at 58 or 59cm, consider XL. If you measured with your hair up in the position you'll wear it, trust the number.

Wool felt is also kinder to hair than you'd expect. It's the main reason people with long hair buy a sauna hat in the first place: dry heat at 80 to 100°C strips moisture from hair and scalp, and covering it is the simplest protection there is [3].

Between sizes

If you're at 59 or 60cm, take M. Two reasons.

First, wool felt has give. Over the first ten or so sessions the fibres relax slightly against the shape of your head, and a hat that started snug settles. A hat that started loose only gets looser.

Second, a snug fit seals the brim against your head, which is what keeps hot air out. Slightly firm beats slightly loose every time.

If you're at 60cm with a lot of hair, XL.

How wool felt changes with wear

New felt is at its firmest. Expect a Halo to feel structured for the first few wears and then ease into your head shape. It won't stretch by more than about half a centimetre, and it won't shrink if you follow the two care rules: never machine wash, never dry it on direct heat. Hang it by the loop and let it air dry. Full details in the care guide.

If you ever want to reshape it, hold it over steam for a few seconds, put it on, and let it dry on your head or on a bowl roughly your head size.

Still not sure

Every Halo ships with a 30-day money-back guarantee, and that includes swapping sizes. Order the size the tape tells you, wear it for a session, and if it's wrong we'll swap it. The sauna hat FAQs cover the other common questions, or go straight to the Halo sauna hat and pick your size.

Sources

1. Ball R, Shu C, Xi P, Rioux M, Luximon Y, Molenbroek J. A comparison between Chinese and Caucasian head shapes. Applied Ergonomics. 2010;41(6):832-839. (Adult head circumference distributions.)
2. Bushby KM, Cole T, Matthews JN, Goodship JA. Centiles for adult head circumference. Archives of Disease in Childhood. 1992;67(10):1286-1287.
3. Lee Y, Kim YD, Hyun HJ, Pi LQ, Jin X, Lee WS. Hair shaft damage from heat and drying time of hair dryer. Annals of Dermatology. 2011;23(4):455-462. (Effects of heat exposure on hair shaft structure.)

Written by Liam Connors, founder of Halo. About Halo.