Huberman-Approved Gym Kit? Here's What He'd Actually Wear
Morning light. Cold plunge. Sleep temperature to the degree. The optimisation crowd has covered almost every input going.
Clothing is the one nobody talks about, despite being worn for more hours than any protocol on the list is practised for, at the exact point body temperature is highest and skin is most permeable.
So here is what the reasoning actually points at.
The blind spot in an otherwise complete protocol
Sunlight in the first hour. Deliberate heat and cold. Caffeine timing. Sleep environment down to the degree. Every input measured, sequenced and tested.
Then a pair of shorts spun from petroleum, worn for an hour, at the point body temperature peaks and pores are widest.
It is not an oversight. Activewear is sold on colour and stretch, so the conversation never reaches the fibre. Nobody has put the question in front of the people who would care most about the answer.
You can track your sleep to the minute and still train in plastic for an hour a day.
Three principles, applied to fabric
Deliberate, not accidental
The whole point of sauna and cold exposure is that temperature is applied on purpose. Polyester is dense and non-porous, so it holds heat against the skin whether you want it there or not. Merino regulates in both directions instead.
Environmental load
A 2024 study found microplastics in every human testicular sample tested, and they have been found in blood and lung tissue. PET was among the most common polymers. It is also what most gym kit is made from.
Ask how it works
Quick-drying means the fibre cannot absorb, so sweat sits on the skin while the fabric dries around it. Merino takes moisture into the fibre core and releases it as vapour. Same claim on the label, opposite mechanism underneath.
What the research actually shows
Heat is the mechanism nobody disputes. Sperm production needs a temperature a couple of degrees below the rest of the body, which is why the anatomy sits outside it.
In a study of 656 men, those in loose, breathable underwear had 25% higher sperm concentration than men in tighter synthetics. That study compared fit rather than fabric, but the mechanism it demonstrates is heat.
Antimony trioxide is the catalyst used to make most polyester and is present in 80 to 85% of virgin PET. Lab testing found 125 to 470 µg/g in finished fabric, a fraction of which migrated into artificial sweat.
Where to start
It is held against the skin for the entire session and it is synthetic mesh on almost every short sold, even when the shell is not. Changing the outer fabric does nothing if the liner stays the same.
The layer worn longest and thought about least. Organic cotton, no elastane, nothing synthetic against the skin at all.
Five per cent elastane still sheds, still traps heat, and still decides how long the garment lasts. A number next to a synthetic is not a compromise, it is a plastic.
The input nobody optimised
Nero shorts use a 100% GOTS organic cotton shell and a 100% merino liner at 17.5 micron. No polyester. No nylon. No elastane. The drawcord is cotton.
Two fibres from the earth, no plastic between them.
Shop Merino Liner ShortsThe short version
Take the principles the optimisation crowd already runs on, heat as a deliberate lever, reducing environmental load where you can, and judging a thing by its mechanism rather than its marketing, and apply them to what sits against your skin for an hour a day.
They land on natural fibre. Merino regulates temperature in both directions, absorbs moisture into the fibre rather than leaving it on the skin, and sheds no microplastics. Organic cotton handles the outside. Neither is the cheap option, which is precisely why almost nobody uses them.
The full research on hormones and synthetic fabric is on our testosterone page, and the shorter version in is polyester bad for testosterone.