THE SCIENCE
The science of keeping them cool.
Your testicles are built to run 4 to 7 degrees cooler than the rest of your body. Here's what happens when your underwear takes that away, and how Kelvin gives it back.
WHY TEMPERATURE MATTERS
They hang outside your body for a reason.
Sperm production is one of the most heat-sensitive processes in the human body. That's why your testicles sit outside it, 4 to 7 degrees cooler than your core. Standard underwear presses them back against 98.6°F skin, and hours of sitting trap the heat even further. You can't feel it, but the research can measure it.
+25%
Higher sperm concentration in men who wore looser, cooler underwear, compared with men in tight underwear, in a Harvard study of 656 men.
Harvard T.H. Chan School of Public Health, Human Reproduction, 2018
−52%
Drop in average sperm concentration between 1973 and 2011 among men in North America, Europe and Australia.
Levine et al., Human Reproduction Update, 2017
3 months
Of regular sauna sessions were enough to significantly impair sperm production in healthy men. The effect reversed after the heat stopped.
Garolla et al., Human Reproduction, 2013
AND YOUR TESTOSTERONE
The same organs that make your sperm also produce most of your testosterone. Meanwhile, average testosterone levels in American men have fallen across generations, independent of age. Keeping the factory in the conditions it was built for is the simplest thing you can control.
THE GOOD NEWS
Heat damage isn't permanent. In a clinical study, cooling the scrotum every night for 12 weeks led to a significant increase in sperm concentration and total sperm count in men with low sperm counts.
THE TECHNOLOGY
Built for space. Rebuilt for your boys.
In 1987, NASA's Johnson Space Center began working on a way to protect astronauts from the extreme temperature swings of space. The answer was phase-change technology: microscopic capsules that absorb heat when it rises and release it when it drops, with no power source and nothing to switch on. Kelvin re-engineered it for the most heat-sensitive organs you own. We call it the Thermal Set Point™ System.
Think of an ice cube in a drink: as long as it's melting, it absorbs the heat and keeps the drink cold. Our fabric holds millions of microscopic capsules that do the same thing, calibrated to react at 93°F, the temperature your boys are built for.
YOU HEAT UP
The moment the temperature down there climbs past 93°F, the capsules start to melt and soak up the excess heat.
THEY HOLD IT
Instead of building up against your body, the heat stays locked inside the capsules.
YOU COOL DOWN
As soon as you cool off, the capsules solidify again, release the heat and reset. All day, on their own.
THE DIFFERENCE
Wicking reacts. Phase-change prevents.
Most "cooling" underwear relies on wicking fabrics. They wait for you to sweat, then move the moisture away. By then, the heat has already built up. The Thermal Set Point™ System works earlier: it absorbs excess heat before it has a chance to build, and ultrafine merino handles whatever moisture is left.
WICKING FABRICS
- React after you sweat
- Heat builds first, then gets managed
- Often synthetic: polyester, nylon
THERMAL SET POINT™ SYSTEM
- Acts before heat builds up
- Absorbs excess heat above 93°F
- Paired with ultrafine merino
THE ARCHITECTURE
Engineered down to the last seam.
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THERMAL SET POINT™ SYSTEM
Heat-absorbing microcapsules in the pouch zone, calibrated to 93°F.
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3D CONTOURED POUCH
Holds everything forward and away from your thighs, supported but never pressed against your body.
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ULTRAFINE MERINO
17.5 microns, finer than a human hair, naturally temperature-regulating and odor-resistant.
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TAG-FREE BY DESIGN
A self-fabric covered waistband and flat seams, with nothing between you and the fabric.
OUR SOURCES
Backed by science. Not by marketing.
Every number on this site points to published research. Read it yourself.
Your boys have been running hot long enough.
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