Thermoregulation in clothing: a T-shirt that responds to temperature for you

Thermoregulation in clothing is a fabric's ability to respond to your skin temperature — taking up excess heat before you start to sweat and releasing it when it gets cooler next to your skin. It's different from what most “technical” T-shirts do: they respond to sweat that has already formed. Thermoregulating clothing works earlier — so that less sweat forms in the first place.

On this page we explain how it works in THE IQONE T-shirts, where the technology comes from and in which situations you'll feel the difference most.

What is thermoregulation in clothing?

Your body constantly watches one number: its core temperature. When you step from a cold street into a heated bus, carry shopping up the stairs or sit in a meeting room with broken air conditioning, your body reacts the same way — it widens your blood vessels and starts sweating. That costs energy, and you know the side effects: a damp back, a chill when you go outside, adjusting your layers yet again.

Thermoregulating clothing takes over part of that work. The fabric itself stores surplus heat when there's too much of it and releases it when the temperature next to your skin starts to drop. Your body has fewer reasons to start sweating — and you have fewer reasons to think about what you're wearing.

That's what sets thermoregulation apart from insulation (a jumper or fleece only holds heat in) and from moisture wicking (a classic technical T-shirt only works once you're already sweating).

How Outlast® PCM works

In THE IQONE T-shirts, thermoregulation comes from Outlast® technology, originally developed for NASA. The idea behind it: a material that evens out temperature swings by itself.

At the heart of the technology are phase change materials (PCM) — microscopic capsules containing a substance that melts and solidifies at a temperature close to that of your skin. When you get warmer, the substance in the capsules melts and absorbs heat as it does so (just as melting ice cools a drink). When you start to get cooler, the substance solidifies and gives that heat back. The capsules are embedded in the viscose fibre itself, not applied to the surface — they won't wash out or wear off.

It's important to get this right: the fabric works with the temperature of your skin, not the temperature around you. That's why the same T-shirt works on the trail, in the office, in a heated car and on a walk — it responds to what's happening to you, not to the weather.

A measurable effect: according to Outlast® data for PCM technology (measured by the independent INSIDE CLIMATE laboratory in Munich), the amount of moisture on the skin drops by up to 50% compared with a fabric without PCM. We write more about this figure and the research behind it in Up to 50% less sweat — where the figure comes from, and about the technology itself in our guide to PCM.

When you'll feel the difference most

Thermoregulation is always working, but on some days you clearly feel it. What those days have in common is change. Moving, stopping, moving again; changes of surroundings, pace and load — everything that normally ends with a damp back or reaching for another layer.

Trail and trekking: climb, stop, descent

On the climb you warm up and sweat, at a stop on the ridge the wind quickly chills your back, and down in the valley the sun is warm again. A PCM T-shirt takes up excess heat as you climb and gives it back when you stop. Less taking layers on and off, less getting chilled at stops — and on a multi-day route, a T-shirt that doesn't pick up odour.

A day when your surroundings change a dozen times

Home, a heated car, the car park, a shop, the office, a meeting room, the car again. Every move is a jump in temperature that an ordinary T-shirt responds to late — first too warm, then too cold. A thermoregulating T-shirt evens out these jumps as they happen. For many of our customers, this is the moment they notice: you stop taking a jumper on and off.

Under a jacket or blazer

An outer layer holds heat in but can't tell “nice and warm” from “too much”. A PCM T-shirt worn directly against the skin takes up the excess under the jacket and gives it back when you take the jacket off. The result: less sweating inside, less chill outside. How to layer under a jacket.

Stop-start effort: work, walks, training with breaks

Walking the dog and stopping for a chat. Carrying boxes, then half an hour at the desk. Warm-up, a set, a break. With this rhythm, ordinary fabrics can't keep up — they're too warm when you stand still and get wet when you move. PCM works as a buffer: it collects heat during effort and gives it back when you rest.

Long hours with no chance to change

A business trip, a full day at clients, a long journey, work in the field. What matters here is not just temperature but also a T-shirt that looks and smells after 10 hours the way it did in the morning. Less sweat means less odour, and Tencel™ handles moisture well. We write about this in Why THE IQONE T-shirts don't pick up odour.

Changing climates and long expeditions

Marek Kamiński crossed Patagonia and reached both poles in a THE IQONE T-shirt — routes where conditions change from hour to hour and changing clothes isn't an option. It wasn't a lab test, but weeks of non-stop wear. The story of this partnership is, for us, the best proof of what “evens out instead of reacting” means.

Thermoregulating vs thermoactive — what's the difference?

The two terms are often treated as synonyms. They aren't.

A thermoactive T-shirt wicks moisture. It's made of fibres that don't absorb sweat but let it pass to the outside, where it evaporates. The condition: the sweat has to form first.

A thermoregulating T-shirt limits how much sweat forms. It stores heat before your body decides it needs to cool down, and gives it back when it gets cooler. That's why it works best where movement alternates with standing still and the temperature keeps changing.

If you're looking for a T-shirt for a day when movement alternates with standing still — on the trail, in the field or in town — read on. More about materials: Merino or PCM.

What THE IQONE thermoregulating T-shirts are made of

The composition matters, because PCM is only half the story. The other half is the fibre it sits in.

Tencel™ (lyocell) — a fibre made from eucalyptus and beech wood, produced in a closed loop. Smooth to the touch, cool, and good at managing moisture. It's why the T-shirt doesn't itch, doesn't build up static and doesn't pick up odour the way synthetics do.

Outlast® viscose — a cellulose fibre with embedded PCM capsules. This is what stores and releases heat. The capsules are part of the fibre, so they work for the whole life of the T-shirt.

7% Lycra® — so the T-shirt keeps its shape and springs back after a full day.

93% of the fibres are of natural origin, from wood cellulose. We didn't choose this for an “eco” label, but because on the skin, for 10 hours, cellulose behaves better than plastic. More: Fibres of natural origin instead of synthetics. Made in Poland.

Who thermoregulation is for

The same technology, four different days. Choose yours.

A full day on the move — office, car, city

Meetings, shopping, the school run, a walk. A T-shirt that doesn't make you think about layers from morning to evening. Women's thermoregulating T-shirt — for the office, walks and travel · A layer under your jacket · Sweating at the office — what to wear · A T-shirt for changeable weather · Long car journeys.

Working in the field

Service engineers, sales reps, technicians, site managers — car, warehouse, client's office, car again, for 10–12 hours. The Worker collection has a roomier cut and a longer back, and we make branded versions for companies. Clothing for field service engineers · What a field sales rep wears: car, client, car · Base layers for stalking and the hide · About the Worker collection.

Outdoors and sport in changeable weather

Trekking and trails, a morning run, cycling, tennis, the gym with breaks between sets. Anywhere movement alternates with standing still and the weather isn't constant. Expeditions · Running · Tennis · Gym.

You want to understand the technology

How PCM works · From NASA to a T-shirt · Merino vs PCM · Polyester vs Tencel.

Frequently asked questions about thermoregulation

Is a thermoregulating T-shirt the same as a thermoactive one?

No. A thermoactive T-shirt wicks away sweat that has already formed. A thermoregulating T-shirt stores excess heat so that less sweat forms, and gives it back when it gets cooler. It works best where movement alternates with standing still: on the trail, in the field and through a whole day in town.

How long does the thermoregulation effect last?

PCM capsules work in a cycle: they absorb heat when you get warmer and give it back when you cool down. On a typical day — moving between rooms, activity with breaks — the cycle repeats many times, so the effect lasts for as long as you wear it.

Does the T-shirt respond to the outside temperature?

It responds to the temperature of your skin. That's why it works the same in a heated car as in a chilly car park — it doesn't care about the weather, only whether you're too warm or too cold.

Does it work under a jacket or blazer?

Yes — and that's one of the places where it works best. The outer layer holds heat in, and the T-shirt absorbs the excess before you start to sweat. Wear it directly against your skin.

Is it suitable for trekking?

Yes. Climb, stop, descent is exactly the rhythm in which PCM has the most to do: on the move it takes up excess heat, at a stop it gives it back. Wear it as your first layer, under a fleece or jacket.

Is it suitable for the office?

Yes. The Sport cut looks like an ordinary, well-cut T-shirt, and Tencel™ doesn't build up static or shine like polyester. Wear it under a shirt, under a blazer or on its own.

Does it pick up odour?

Much less than synthetics. Less sweat and less moisture in the fabric mean less odour. Many customers wear the T-shirt several days in a row without washing it.

How do I wash a PCM T-shirt?

At 40 °C (maximum 40 °C), spin at up to 1000 rpm, with a mild detergent — the fewer chemicals, the better. No fabric softener (it makes the fibres stick together) and no tumble dryer. Dry naturally — on a hanger, a drying rack or flat, away from radiators. Iron at 100 °C max. The PCM capsules are part of the fibre — they won't wash out. Full care guide.

THE IQONE thermoregulating T-shirts

• Sport Tee Women's — short sleeves, women's cut, for every day, the trail and sport.
• Sport Tee Men's — short sleeves, men's cut.
• Sport Longsleeve Women's / Men's — long sleeves for cooler days, the trail and under a jacket.
• Worker / Worker Longsleeve — unisex, roomier cut, longer back; for work and for companies.
• Thermoregulating Headband — the same technology at your forehead; most often bought together with a T-shirt.

Made in Poland. Composition: 56% Tencel™, 37% Outlast® viscose, 7% Lycra® — 93% fibres of natural origin (wood cellulose).