The dirty secret the activewear industry doesn't want you to know...
Why You Should Never Wear Polyester In the Sauna
Brian S.
Wellness Researcher
Plastic shorts are bad enough. But in the sauna? Even worse. Microplastics. Toxic chemical leaching. Not something you want on your skin.
Your sauna session is a great time to relax and think.
But here's something most guys don't think about: what they're wearing while they're doing it.
If you're like most guys, you step into the sauna in a pair of athletic shorts — the same ones you'd wear to the gym. And those shorts are almost certainly made from polyester.
That's a problem. A much bigger problem than most people realize.
Polyester is plastic. It's made from the same petroleum-based compounds used to make plastic bottles and food packaging. At room temperature, it sheds microscopic plastic fibers onto your skin and slowly off-gasses chemical compounds from the fabric.
But in a sauna — at 150°F to 200°F+ — those processes don't just continue. They accelerate. Dramatically.
You're essentially sitting in a hot box, wrapped in plastic, with every pore on your body wide open.
What Heat Does to Polyester - And To You
Most of the concerns about polyester activewear are based on normal wear conditions — room temperature, moderate activity. The sauna changes every variable in the wrong direction.
1. Heat accelerates chemical off-gassing.
Polyester fabrics often contain BPA, phthalates, and are frequently treated with PFAS ("forever chemicals") to create moisture-wicking properties. At room temperature, these chemicals leach slowly. But research on plastics has consistently shown that heat dramatically increases the rate of chemical migration. It's the same reason you're told never to microwave food in plastic containers or leave plastic water bottles in a hot car. The chemistry doesn't change just because the plastic is shaped like shorts instead of a bottle. At sauna temperatures, you're supercharging the release of every chemical compound in that fabric.
2. Your pores are fully open.
The entire point of a sauna is to induce deep sweating. Your skin temperature rises, blood vessels dilate, and your pores open wide. This is the mechanism that makes saunas therapeutic — but it also makes your skin maximally absorptive. Research published in Environmental Science & Technology has shown that scrotal skin is already among the most permeable areas of the male body under normal conditions. In a sauna, with elevated skin temperature and fully dilated pores, the absorption rate increases further. You're creating the ideal conditions for chemical transfer from fabric directly into skin tissue.
3. Microplastic shedding increases with heat and friction.
Polyester sheds microscopic plastic fibers during normal wear. Studies on microplastic release from synthetic textiles have shown that higher temperatures increase fiber shedding. In a sauna, you're combining extreme heat with the friction of sitting, shifting, and sweating against a wooden bench — all of which accelerate the breakdown and release of plastic microfibers directly onto your skin.
4. You're supposed to be detoxing — not adding toxins.
This is the cruel irony. Many men use the sauna specifically for its detoxification benefits — sweating out heavy metals, clearing metabolic waste, supporting the body's natural elimination pathways. But if you're wearing polyester while you do it, you may be simultaneously absorbing the very types of synthetic chemicals you're trying to eliminate. The sauna is one of the most powerful health tools available. Wearing plastic while you use it undermines the entire purpose.
The Blind Spot In Your Sauna Protocol
Think about everything you've dialed in.
You know the optimal temperature range. You've figured out your session length. Maybe you alternate with cold plunge. You hydrate with electrolytes before and after. You've probably read at least one study on heat shock proteins.
You care about what goes into your body. You filter your water. You read labels. You avoid processed food. You'd never drink from a plastic bottle that had been sitting in a 180°F car.
But every time you step into the sauna, you wrap the most absorptive, temperature-sensitive tissue on your body in petroleum-based plastic fabric — and sit in extreme heat for 10 to 30 minutes.
Your skin is wide open. The chemicals are mobilized. And you're doing this on purpose, multiple times a week, because you believe it's making you healthier.
It's the one protocol variable nobody's optimized. And once you see it, you can't unsee it.
So What Should You Actually Wear in the Sauna?
Some guys go no-shorts in a private sauna — just a towel. That works if you have your own setup at home. But if you're at a gym, a spa, a bathhouse, or sharing the space with anyone else, you need shorts.
The answer is the same one that existed for thousands of years before synthetic fabrics were invented: natural fibers. Cotton and wool don't shed microplastics. They don't contain BPA or PFAS. They don't off-gas chemical compounds when exposed to heat. They're what your body was designed to be in contact with.
The problem has been finding natural fiber shorts that actually fit and perform like modern activewear — most "natural" brands make products that feel more like burlap than Lululemon.
One brand that's built specifically for this is Ryker. They make athletic shorts from 100% organic cotton with a 100% merino wool built-in liner — and they've become particularly popular with the sauna community for reasons that go beyond just avoiding plastic.
What Makes Ryker Different
Ryker's approach is straightforward: replace synthetic fabrics with natural alternatives that perform better - and aren't loaded with toxins.
The outer short is made from 100% GOTS-certified organic cotton. It's soft, breathable, and surprisingly stretchy thanks to a specialized knitting technique that gives natural cotton the flexibility you'd normally need spandex for. No polyester. No nylon. No spandex. Nothing that off-gasses in sauna heat.
The built-in liner is where it gets interesting. Instead of the standard polyester mesh compression liner found in virtually every major activewear brand, Ryker uses 100% merino wool. Merino is naturally temperature-regulating — it works with your body in the sauna rather than trapping heat against your skin. It wicks moisture naturally without chemical PFAS coatings, and it's naturally antimicrobial, meaning it doesn't breed bacteria even after multiple sauna sessions.
Third-party tested. Every batch of Ryker's fabric is independently lab-tested and certified free of BPA, PFAS, phthalates, and formaldehyde. They hold both GOTS and OEKO-TEX Standard 100 certifications. At any temperature — room temp or 200°F — there's nothing in this fabric that can leach into your skin.
And they actually fit like Lululemon or Vuori — same athletic cut, zipper pockets, range of inseams. You wouldn't know they were natural fiber by looking at them or wearing them. You'd only know by what's not happening against your skin.
Over 100,000 pairs sold · 4.9-star average across 5,000+ reviews · Endorsed by Ben Greenfield and a growing list of health-focused creators.
How They Compare
Fabric
Toxic Chemicals
In Sauna Heat
Microplastic Exposure
Odor After Sauna
100% organic cotton +
100% Merino wool
3rd party tested + OEKO-TEX Certified
Natural fibers — no chemical leaching at any temp
Protects from Microplastics
Naturally antimicrobial — wear multiple sessions
"The Other Guys"
100% Plastic (polyester, nylon, spandex)
Often contains high levels of BPA, Phthalates and PFAs
Heat accelerates chemical off-gassing from plastic fabric
Loaded with Microplastics
Bacteria breeds in trapped heat and moisture
The choice is clear - you shouldn't be wrapping yourself in toxic plastic shorts all day.
Natural Fiber Gym Shorts With A Compression Liner
The Apex Short - (100% Organic Cotton + 100% Merino Wool Liner)
100% organic cotton outer short + 100% organic Merino wool liner
Organic cotton from GOTS-certified sources + fabrics from OEKO-TEX certified partners
Fits just like Lululemon shorts
Naturally stretchy, temperature regulating and odor resistant
$66.00
$89.10
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100% Natural Fibers
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Description
- 100% organic cotton outer short + 100% organic Merino wool liner
- Organic cotton from GOTS-certified sources
- OEKO-TEX Standard 100 certified fabrics & dyes
- Our fabrics are 3rd party tested BPA, PFAS and phthalate free - see report here.
- Our Merino wool is not superwashed - we use an innovative new GOTS compliant process that uses ozone to descale our wool, giving it a level of machine washability. Learn more here.
Enough with the polyester shorts with the toxic liners. Switch to Apex shorts made with natural fibers.
Guaranteed to be the most comfortable gym short you've ever worn.
Size Chart
NEW SIZING: RUNS LARGE - SIZE DOWN FOR A PERFECT FIT
Materials and Care
Shorts: 100% Organic Cotton
Liner: 100% Organic Merino Wool
Care Instructions: Machine wash on cold with gentlest setting available. Wool specific setting if possible. Gentle washing avoids felting and shrinking.
Lay flat to dry. Do not tumble dry.
Wash only when needed - Merino naturally avoids odor, meaning less washing is needed!
Shipping & Returns
FREE Shipping on orders $150+.
If you don't love it, return it (unused) in 90 days for a full refund.
Care Instructions
Cold wash & hang to dry.
Trusted By Top Health Experts And Biohackers
Why High Performers Are Switching...
MH
Mark H.
Founder & CEO
Miami
I optimize everything else. This was my one blind spot.
"I spend $600/month on supplements, recovery, and bloodwork. I track every input that goes into my body. Then I realized I was spending 4 hours a day training in petroleum-based plastic that's been linked to hormone disruption. Once I saw the data on polyester and endocrine disruptors, I couldn't unsee it. Switched to Ryker, and I won't go back. These are now a non-negotiable in my protocol."
MH
William T.
Managing Director
New York
I looked at the research. The decision was obvious.
"I don't buy anything based on marketing alone. I looked at the actual studies on polyester, microplastics, and BPA - and the data is hard to argue with. Ryker's third-party lab results showing zero endocrine disruptors sealed it for me. The Merino liner is genuinely more comfortable than any synthetic I've worn. These are the only shorts I train in now."
MH
James G.
VP, Technology
San Francisco
The last gap in my health stack.
"Eight Sleep, WHOOP, my sauna - I've invested in all of it. But I was still training in polyester shorts that shed microplastics. It's absurd when you think about it. Ryker closed the last gap. The fit is identical to Lululemon, the Merino liner handles sweat better than any synthetic, and I'm not absorbing endocrine disruptors through my skin for two hours a day. Should've done this years ago."
Done wearing plastic to the gym?
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