Bryan Johnson-Approved Gym Kit? Here's What He'd Actually Wear
He measures over a hundred biomarkers. He publishes the entire protocol for free. He has a number for the speed at which his own body is ageing.
Apply that level of scrutiny to the thing pressed against your skin for an hour a day and you end up somewhere fairly specific.
Measure everything, including the inputs nobody measures
The Blueprint approach is not really about supplements. It is about treating every input as measurable, then removing the ones that carry a cost and keeping the ones that do not.
Diet, sleep, light, exercise, and increasingly what is in the environment rather than what goes in the mouth. Air, water, containers, packaging.
Clothing sits in that same category and almost nobody audits it, despite being worn for more hours than any protocol on the list is practised for.
You can filter your water and still sweat into a plastic bottle for an hour a day.
Three principles, applied to fabric
Remove what carries a cost
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 found. It is also what most gym kit is made from.
Dose is hours, not milligrams
Antimony trioxide is the catalyst used to make most polyester and sits 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 under standard conditions.
Mechanism, not marketing
Quick-drying means the fibre cannot absorb, so sweat sits on your skin while the fabric dries around it. Merino takes moisture into the fibre core and releases it as vapour. Same word on the label, opposite process underneath.
The part of the protocol worn against skin
Heat is the mechanism nobody argues with. Sperm production runs a couple of degrees below core body temperature, 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 compared fit rather than fabric, but the mechanism it demonstrates is heat, and polyester is engineered to hold heat against the skin.
Merino regulates in both directions instead. It absorbs moisture into the fibre core and releases it to the air, and holds odour compounds inside the fibre rather than on the surface where bacteria reach them.
What the reasoning points at
Held against the skin for the entire session, and 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 audited 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 audited
Nero shorts use a 100% GOTS organic cotton shell and a 100% merino liner at 17.5 micron, from RWS certified farms. 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 measurement crowd already runs on, audit every input, reduce environmental load where you can, and judge a thing by its mechanism rather than its claim. Then apply them to the fabric held 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 your skin, and sheds no microplastics. Organic cotton handles the outside. Neither is the cheap option, which is precisely why almost nobody uses them.
Same reasoning applied elsewhere in the Huberman version, and the full hormone research on our testosterone page.