Your underwear
is suppressing
your testosterone.
Polyester traps heat. Heat downregulates Leydig cell function. Phthalates leach into the scrotal microenvironment and suppress free testosterone with every doubling of exposure. KRYOS is engineered around the science your underwear has been ignoring.
Three mechanisms. One garment.Compounding daily.
Thermoregulatory failure
Synthetic fibres trap heat against the scrotum. Sustained elevation above 35°C suppresses spermatogenesis and reduces Leydig cell testosterone output. Most polyester briefs measure 2–4°C above this threshold within an hour of wear.
Endocrine-disruptor leaching
Polyester is plasticised with phthalates. Body heat and sweat extract them through the inguinal skin — among the most permeable tissue on the body. Every doubling of urinary phthalate metabolites correlates with a measurable drop in serum testosterone.
Mechanical compression
Athletic-cut briefs without anatomical relief compress the pampiniform plexus — the venous network that cools arterial blood entering the testes. The result is a small but chronic ischemic load with downstream effects on both T and sperm quality.
Engineered against your endocrine system —not for it.
Two fibres. Each selected for a measurable property — moisture transport rate, thermal conductivity, plasticiser-free polymer chemistry. No filler. No polyester at any stage of spinning, weaving, dyeing, or finishing. Audit trail available on request.
Zero polyester
No synthetic fibres. No endocrine disruptors. No plastics against your skin.
Precision cooling
Micro-perforated TENCEL™ cooling knit covers the full front zone. Natural-fibre thermodynamics maintain optimal scrotal temperature passively — every hour, every day.
OEKO-TEX certified
Every component tested and certified free of harmful substances. FSC-certified TENCEL™ sourcing. No toxic dyes. Clean from fibre to finish.
3D anatomical design
Forward-projecting contour pouch creates separation without compression. Air circulates freely. Heat has nowhere to accumulate.
Every other underwear is built for the aesthetic, not your health.
| Criterion | KRYOS Model 001 |
Mack Weldon AIRKNITx |
Tom Ford Cotton brief |
SAXX Vibe modal |
|---|---|---|---|---|
| Polyester content | 0.00% | 52% | 0% | 7% |
| Phthalate-free certification | Audited | — | — | — |
| Scrotal temp reduction | −4.0°C | −1.1°C | −2.8°C | −1.6°C |
| Endocrinologist review | Yes · on file | — | — | — |
| Anatomical pouch (3D) | ● | ○ | — | ● |
| Micro-perforated cooling | ● | — | — | — |
| Price | $44 | $28 | $45 | $36 |
Reviewed by physicians.Not influencers.
Two practising clinicians reviewed our material claims, the underlying studies, and the manufacturing audit before KRYOS went into production. Neither receives equity. Both retain right of refusal on any future product line.
"In two decades of male endocrine practice I have written the same one-line recommendation to almost every patient: switch to natural-fibre, looser-cut underwear. KRYOS is the first product I have seen that engineers for that recommendation specifically."
"Testosterone is not a vanity hormone. It is structural to cardiac muscle health, lipid metabolism, and vascular tone. Anything that depresses it daily is a cardiovascular risk factor. This is the first underwear I have endorsed."
What men report.
"Free T came back at 712 on my Q1 panel — up from 548 the year before. Only variable I changed was underwear. I am aware this is anecdote, not RCT. But the trend is hard to ignore."
"The Whoop strain data tells the story. Recovery improved by 8 points on average. Sleep latency dropped. I did not expect underwear to do that and I cannot explain it any other way."
"Skeptical to begin with. The product feels like nothing — no waistband bite, no heat, no shift. Aesthetically it is the cleanest pair I have owned. The science either works or it does not. I want it to."
"I run an AG1 / Whoop / Function stack. KRYOS slotted in cleanly. The infographic on the box is the kind of detail I want. Other brands send a thank-you card. This sent a spec sheet."
"Knocking one star because I want a longer leg option. The fabric and pouch are correct. I am 45 and have not had a pair I would write about — until this one."
You have questions.So did we.
If yours is not below, write to support@kryos.co — answered by a human within 24 hours.
01Is the testosterone effect actually causal? +
02What's wrong with my current underwear? +
03Why $44? +
04Where is it manufactured? +
05Why only one colour and one cut? +
06What if it doesn't work for me? +
Wear better.
Test in 90 days.
Pull a baseline panel today. Switch to KRYOS exclusively. Pull a follow-up panel at 90 days. Decide for yourself.