I'm interested

In development — help shape the first drop

Engineered for
thermal balance.

I'm building NordKyl: thermal and cooling activewear for training in the cold and recovering after the sauna. Before anything launches, I want to hear which pieces you'd actually wear, and what they'd be worth to you.

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Your opinion matters to me.

I'm building NordKyl on my own, and your answers decide what actually gets made. Tell me which pieces you'd wear and what you'd honestly pay for them.

As a thank-you, you'll get 10% off your first order. Your code appears right after you send your answers.

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SaunaNordKyl Cooling Underwear

NordKyl Sauna Cooling Underwear

Get the most out of your sauna.
Without overheating what matters.

The sauna does a lot for your body. But your testicles work best 2⁠–⁠4 °C cooler than the rest of you, and research links repeated heat exposure to lower sperm quality. NordKyl sauna underwear puts a reusable cooling gel pack right where the heat hits hardest, so the rest of you can enjoy the full heat.

Full-body heat. A cool zone where it counts.

I'm interested See the science

The science behind the cooling zone

What nobody tells you about the sauna

01−14%

Sperm production per extra 1 °C

Your testicles need to stay 2⁠–⁠4 °C cooler than your core body temperature to work properly. Studies link every 1 °C rise in testicular temperature to roughly 14% lower sperm production — and to weaker sperm motility.

02

Heat vs. testosterone

Testosterone is made by Leydig cells inside the testicles. Research — mostly in animals so far — shows that heat stress can disrupt these cells and their hormone production. The human evidence is still limited, but the picture is consistent: the testicles work best when they stay cool.

03

No more trade-offs

Our reusable cooling gel insert sits exactly where the heat matters and acts as a cool buffer between you and the hot sauna air. The rest of your body still gets the full sauna experience.

Sources

Based on peer-reviewed studies available through the National Center for Biotechnology Information (NCBI), U.S. National Library of Medicine.

Read the studies:Study 1Study 2Study 3Study 4Study 5Study 6

NordKyl underwear is not a medical device and is not intended to diagnose, treat or prevent any condition. If you're trying to conceive or have concerns about your fertility or hormones, talk to a doctor.

01

Look around

Browse the first NordKyl pieces below.

02

Tap “I'm interested”

Pick anything you'd want and tell me what you'd honestly pay for it.

03

Get 10% off

Leave your email once and get your 10% thank-you code. I'll let you know when your picks are ready to order.

The first pieces

Would you wear this?

Tap “I'm interested” on anything you'd want and tell me what you'd pay for it. Then leave your email once, at the bottom.

Recovery
NordKyl Cooling Underwear
NordKyl Cooling Underwear
NordKyl Cooling Underwear
NordKyl Cooling Underwear

NordKyl Cooling Underwear

The ultimate cooling biohack for your recovery routine — and your most heat-sensitive zone.

Cooling boxer briefs with a reusable gel cooling pack that draws heat away from the groin. The compression fabric and ergonomic cut fit close to your body and keep the pack in place, so your most heat-sensitive zone stays cool in the sauna and after training.

Why you'd want it

  • Reusable gel cooling pack draws heat away from the groin
  • A cooling biohack for your post-sauna and post-training routine
  • Keeps the testicles cooler while the rest of you takes the heat
  • Premium compression with zero restriction on movement

No payment. You'll leave your email once, below.

Men's
NordKyl Thermal Vest
NordKyl Thermal Vest
NordKyl Thermal Vest
NordKyl Thermal Vest
NordKyl Thermal Vest

NordKyl Thermal Vest

Warm up faster and get more out of every session with an advanced thermal layer.

Premium compression vest with a built-in thermal layer. The flexible fabric hugs your torso ergonomically and holds in body heat for a more intense sweat and a more effective workout.

Why you'd want it

  • Thermal layer traps heat for maximum sweat
  • Speeds up your warm-up and intensifies your training
  • Premium compression supports your core
  • Ergonomic cut for complete freedom of movement

No payment. You'll leave your email once, below.

Women's
NordKyl Women's Thermal Vest
NordKyl Women's Thermal Vest
NordKyl Women's Thermal Vest

NordKyl Women's Thermal Vest

Warm up faster and get more out of every session with an advanced thermal layer.

Premium compression vest with a built-in thermal layer. The flexible fabric hugs your torso ergonomically and holds in body heat for a more intense sweat and a more effective workout.

Why you'd want it

  • Thermal layer traps heat for maximum sweat
  • Speeds up your warm-up and intensifies your training
  • Premium compression supports your core
  • Ergonomic cut for complete freedom of movement

No payment. You'll leave your email once, below.

Men's
NordKyl Thermal Shorts
NordKyl Thermal Shorts
NordKyl Thermal Shorts
NordKyl Thermal Shorts
NordKyl Thermal Shorts

NordKyl Thermal Shorts

Warm up faster and get more out of every session with an advanced thermal layer.

Premium compression shorts with a built-in thermal layer. The flexible, high-waisted fabric hugs your body ergonomically and holds in body heat for a more intense sweat and a more effective workout.

Why you'd want it

  • Thermal layer traps heat for maximum sweat
  • Speeds up your warm-up and intensifies your training
  • Premium compression supports your core
  • Ergonomic cut for complete freedom of movement

No payment. You'll leave your email once, below.

Women's
NordKyl Women's Thermal Shorts
NordKyl Women's Thermal Shorts
NordKyl Women's Thermal Shorts
NordKyl Women's Thermal Shorts
NordKyl Women's Thermal Shorts

NordKyl Women's Thermal Shorts

Warm up faster and get more out of every session with an advanced thermal layer.

Premium compression shorts with a built-in thermal layer. The flexible, high-waisted fabric hugs your body ergonomically and holds in body heat for a more intense sweat and a more effective workout.

Why you'd want it

  • Thermal layer traps heat for maximum sweat
  • Speeds up your warm-up and intensifies your training
  • Premium compression supports your core
  • Ergonomic cut for complete freedom of movement

No payment. You'll leave your email once, below.

About

The person behind NordKyl

NordKyl is a one-person project. Here's who's behind it, and why it exists.

Martin, founder of NordKyl

Hello, and thank you for being here — I really appreciate it.

Who I am

My name is Martin Světlík, and I come from a good family in the middle of Europe. NordKyl exists because I'm ambitious, and this is my first real project — one I'm determined to see through from start to finish.

Where it started

My passion for building something of my own goes back to when I was around twelve years old. Designer sneakers were everywhere at the time, and I fell in love with them, even though as a kid they were completely out of my budget. Looking for a way in, I discovered the sneaker resale community and learned about "drops": limited releases sold at retail price, with demand far outstripping supply. That was my first real look at how people made money, and I was hooked.

Over the next few years, I had some genuine luck with it. There's no feeling quite like making 500 euros in three hours as a teenager. But that world eventually changed as cheap, high-quality replicas flooded the market, and sneakers lost much of their value as an opportunity.

Why NordKyl

After that, I had countless ideas for how to build something else. Most of them stayed just that: ideas. The ones I did try, I usually abandoned within a few days. Then in 2025 I graduated and realized I hadn't actually finished anything — and that it was time to change that.

That's when this idea came to me, and I told myself I had to take it from 0 to 100%. It needed to be finished, no matter what.

Honestly, the result almost doesn't matter to me. Even a single order would mean more than most people might expect — it would mean I finally saw something through.

Thank you for being here, and for being part of it.
— Martin

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