The sauna is supposed to be relaxing. Standing outside the door wondering whether you're allowed in wearing a bikini? Less so.
The short answer
What should you wear in a sauna? Follow the facility's dress code. In many US gyms and contrast therapy studios, a swimsuit is the simplest choice. For private infrared saunas, light clothing or a towel may be fine. In traditional Finnish saunas, nudity is common, although customs vary by venue. Whatever you wear, skip exposed metal hardware and bring a clean towel to sit on.
If you're planning to follow your sauna with a cold plunge, there's one more thing to think about: the fabric. A swimsuit that's perfectly comfortable at the beach might be considerably less charming after two rounds of heat and ice water.
What to wear in different types of saunas
There isn't one global sauna dress code. A few common scenarios:
Gym sauna
A swimsuit, or workout clothes if permitted
At a gym, you're generally better off arriving covered. A simple swimsuit makes sense; some facilities also permit clean sports bras and shorts. Not every gym allows workout clothes inside the sauna, so read the sign before heading in. Sit on a towel, not directly on the bench.
Bathhouse or contrast therapy studio
A swimsuit you can comfortably plunge in
These are the places where you'll probably go straight from sweating to shivering. Check that your suit stays opaque when wet, fits securely, and doesn't have hardware that gets uncomfortably hot. If there's a pool, make sure the suit can handle it too.
Infrared sauna
A towel, swimwear, or light clothing, depending on the studio
Many infrared sauna appointments take place in private rooms, so the rules can be more flexible. A swimsuit is an easy option. A towel or lightweight clothes can work when the studio permits them. Private doesn't automatically mean clothing-optional, though.
Korean spa (jjimjilbang)
The spa's uniform in shared areas
At many Korean spas, the gender-separated bathing areas are nude and the common heated rooms are for the shirt-and-shorts uniform provided at check-in. Bringing your own bikini won't replace the spa's dress code.
Finnish sauna
Often nude, sometimes a towel or swimsuit
Finnish sauna culture is famously relaxed about nudity, but it isn't a universal rule that you must be naked. Visit Finland explains that a towel or swimsuit can be perfectly acceptable. Some individual facilities prohibit swimwear for hygiene reasons, so house rules win.
Hot springs
Swimwear where required, ideally without metal details
Mineral-rich water can be tough on certain metals and garment finishes. Rinse your suit after soaking, and check the spring's rules before you go.
What's the best fabric to wear in a sauna?
Here's where the conversation gets interesting. “Breathable” and “quick-drying” aren't the same thing. Cotton is lovely against your skin in a dry sauna but can feel heavy after a swim. Synthetic swimwear sheds water efficiently, although performance varies by knit. Wool manages moisture in a different way: its fibers can take up water vapor without immediately feeling wet.
| Fabric | What's good about it | What to consider | Best fit |
|---|---|---|---|
| Merino wool | Breathable; manages moisture vapor; naturally odor resistant | Can absorb water and may dry more slowly than synthetic swimwear; construction matters | Sauna and water, when made as swimwear |
| Cotton | Soft, breathable, easy to find | Absorbs a lot of water and can feel soggy after a plunge | Dry sauna or lounging |
| Linen | Airy, breathable, comfortable in heat | Typically less stretchy; not every linen weave is suited to swimwear | Wraps and loose sauna clothing |
| Bamboo viscose | Often soft and drapey | Absorbent; “bamboo” on a label usually means regenerated viscose, not raw bamboo fiber | Robes and cover-ups |
| Polyester / nylon blends | Often stretchy and fast-drying; widely available | Breathability varies; some fabrics retain body odor | Conventional swimwear |
This is a practical comparison, not a laboratory ranking of every fabric. Weight, weave, knit, fit, and finishing all change the result. For wool's moisture and odor properties, see Woolmark's breathability research and its odor-resistance overview.
What not to wear in a sauna
- Exposed metal hardware. Rings, zippers, clasps, and underwire can become unpleasantly hot against skin.
- A suit that's only been tested dry. Water can change a fabric's opacity, fit, and weight. Try a new swimsuit in the shower before its public debut.
- Thick, soaked clothes between rounds. If you're heading into a cold room, a heavy wet outfit can feel miserable.
- Anything the facility prohibits. A beautiful swimsuit won't win an argument with a posted dress code.
A wool swimsuit? Actually, yes.
Before synthetic swimwear became the default, people swam in wool. This isn't a quirky internet invention. In 1915, Jantzen was making wool “swimming suits,” a chapter of swimsuit history documented by the Smithsonian.
To be fair, an early 20th-century wool bathing costume and a modern bikini are very different garments. Old suits could be bulky and frustratingly heavy when wet. Nobody needs to bring that part back.
Wool swimsuits had a moment long before anyone invented spandex. We think they deserve another.
Modern fine merino has a softer hand feel than the coarse wool many people associate with winter sweaters. Wool can take up moisture vapor and resist lingering odor, which makes it interesting for clothes worn close to sweaty skin. Those properties are well documented by Woolmark.
Is it magically cooler than wearing nothing? Of course not. Does it beat every synthetic at drying speed? Also no. The appeal is that you can choose a natural fiber with useful performance properties, provided the swimsuit is designed to be worn in water.
Made for the sauna, worn in the water
Meet our merino bikini
Our Merino Wool Bikini Set uses 100% ultrafine merino wool in a 210 gsm interlock knit. The triangle top ties at the neck and back, while the high-leg bottoms have adjustable side ties. The straps contain enclosed natural rubber elastic rather than conventional synthetic elastic, and there are no metal clasps to get hot.
It's handmade in Türkiye. The fabric is certified to OEKO-TEX® STANDARD 100, Product Class II (certificate 11.HOT.97614). It is knitted and dyed by a GOTS-certified mill (GOTS-20420). That describes the mill's certification, not certification of the finished bikini.
The top and bottoms are available in separate sizes, because having a different size on top and bottom is hardly unusual.
See the merino wool bikini →What to pack for a sauna visit
- A swimsuit if the venue requires one
- A clean towel to sit on, plus a dry one for afterward
- Water for before and after your session
- Sandals if you're walking through shared wet areas
- A robe or something comfortable for the trip home
One non-fashion note worth taking seriously: sauna heat can dehydrate you. Drink water and step out if you feel dizzy or unwell. Cleveland Clinic's sauna guidance has a useful overview of precautions.
How to wash a merino swimsuit
After a pool, ocean swim, or mineral soak, rinse the suit in cool fresh water. Hand wash with a gentle detergent suitable for wool, squeeze out excess water without wringing, and lay flat to dry away from direct heat. Chlorine exposure can wear on fibers over time, so don't leave the suit sitting wet in a gym bag.
A few more sauna clothing questions
Can you wear a regular swimsuit in a sauna?
Usually, yes, where swimwear is allowed. Choose something comfortable without exposed metal hardware, and check the venue's rules.
What should a woman wear in a co-ed sauna?
In many US co-ed saunas, a swimsuit is a straightforward choice. Some gyms allow workout clothes; others don't. Bring a towel to sit on and wear the coverage that feels comfortable to you within the dress code.
Can you wear a sports bra and shorts in a sauna?
Only if the facility permits workout clothes. For a sauna connected to a pool or cold plunge, swimwear is usually the more practical option.
Is merino wool too hot for a sauna?
Not necessarily. A lightweight merino swimsuit isn't the same as a heavy winter sweater. But the sauna is hot regardless of what you're wearing, and fit and fabric weight affect comfort.
Can you wear the same swimsuit in a sauna and cold plunge?
Yes, if your suit is intended for swimming and your facility allows it. Check fit and opacity when wet before taking it out in public.
Does merino dry faster than polyester?
Not as a general rule. Polyester typically absorbs less water and often dries faster. Merino's strengths are moisture-vapor management, natural odor resistance, and the option of a natural-fiber garment.
Do you need underwear under a swimsuit in a sauna?
Generally not. Swimwear is designed to be worn on its own, and another layer can add bulk or retain moisture.
Sources and further reading
- Visit Finland: Your guide to Finnish sauna, sauna customs and clothing.
- Woolmark: Wool is naturally breathable, moisture-vapor behavior.
- Woolmark: Wool reduces body odour, odor-related research.
- Smithsonian Magazine: How bathing suits evolved, historical wool swimwear.
- Cleveland Clinic: Sauna benefits and safety, hydration and precautions.
- Ritual Textiles: Merino Wool Bikini Set, garment specifications and certifications.
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