It’s 35°C outside, you’re sweating through your synthetic T-shirt, and you’re wondering why nobody ever explained any of this to you before. Good news: that’s exactly what this article is about. We’re going to break down the main textile fibres so you finally know which materials keep you cool, which ones to avoid at all costs in the middle of summer, and why the layer closest to your skin deserves a little more attention.
What makes clothing feel hot (or not)
Before getting into individual fabrics, here’s a quick bit of physics that makes all the difference.
Breathability and heat dissipation
How warm a garment feels isn’t just about the fibre it’s made from. The structure of the fabric plays a major role too:
- an airy, open-knit fabric allows air to circulate and body heat to escape
- a dense, tightly woven fabric does the opposite, acting almost like a blanket (even when it’s made from a natural fibre).
The thermal conductivity of the fibre matters as well. Some materials conduct and disperse heat more effectively than others, creating a cooler sensation against the skin.
Fabric thickness and weight matter just as much as the fibre
Beyond the type of fibre, fabric weight (usually measured in grams per square metre) can completely change how a garment feels. The principle is simple: the heavier and thicker the fabric, the warmer it tends to feel, and vice versa. The exact same fibre can produce a cool, breathable garment or a stifling one depending on how lightly or densely it is constructed.
It’s something we take seriously with our organic cotton and Tencel T-shirts: our fabrics weigh 145 grams per m², which puts them on the lighter side. But not too light. A fabric that’s excessively thin can become see-through, lose durability and struggle with repeated washing. The right fabric weight is about finding the balance between staying cool, lasting well and feeling comfortable.
Moisture: the silent enemy
Here’s something that’s often overlooked. It isn’t necessarily the heat itself that makes clothing unbearable; it’s perspiration trapped against your skin. When a fabric absorbs sweat without moving it away from the body, moisture builds up, you feel hotter and bacteria get exactly the environment they need to thrive.
So a fabric that keeps you cool is, above all, a fabric that can pick up moisture and move it away from your skin.
The best fabrics for keeping cool: how they really compare
Linen: the natural champion of summer
You can’t really talk about summer fabrics without starting with linen. Its naturally open fibre structure provides excellent airflow, while its ability to release body heat makes it one of the best-performing natural fibres in hot weather. It can absorb up to 20% of its own weight in moisture without feeling wet against the skin. When it comes to fabrics that don’t make you overheat, linen has more than earned its reputation.
Its one real drawback? It wrinkles. A lot. Enthusiastically. But when you’re dealing with a heatwave, a few creases in your linen trousers are probably the least of your concerns.
Cotton: good, but not quite as perfect as people think
Cotton has a great reputation as a summer fabric, and much of it is deserved. When made into a lightweight fabric, such as fine poplin or lightweight jersey, it really can keep you comfortable in warm weather. It is breathable, soft and reasonably good at absorbing moisture.
There is one catch: cotton absorbs moisture well but takes a relatively long time to dry. In very hot weather or during physical activity, that can quickly leave you with a T-shirt stuck to your back. Not exactly ideal. And as we saw above, the problem becomes even more noticeable with heavier cotton fabrics such as heavyweight jersey, fleece or denim, which absolutely can make you feel hot.
What about organic cotton? Thermally, it behaves much like conventional cotton, but it is grown without pesticides and has a significantly lower environmental impact. For responsibly made clothing, that should really be the baseline. As an added benefit, it is also gentler on sensitive skin.
Tencel (lyocell): the unexpected all-rounder
If Tencel isn’t on your radar yet, it probably should be. Made from wood pulp, this fibre is, in our view, one of the most complete materials available for staying cool. And that isn’t just marketing talk: its properties are documented and measurable.
Tencel is 50% more absorbent than cotton. Its hydrophilic fibres capture moisture and move it quickly towards the outer surface, helping your skin stay dry even as temperatures rise. This rapid moisture management also creates a natural antibacterial effect: without a persistently damp environment, bacteria have less opportunity to multiply and unpleasant odours are less likely to develop.
Add to that genuine thermoregulatory properties (Tencel responds well to changes in body temperature, helping you feel cooler when it’s hot while retaining some warmth when it’s cold), a silk-like lightness, an ultra-soft feel and hypoallergenic properties that make it particularly suitable for reactive skin. That’s a lot for one fibre. But it really does deliver on multiple fronts.
We’ve dedicated a whole series of articles to Tencel if you’d like to explore the subject in more detail:
- What is Tencel?
- Thermoregulating underwear: the secret to lasting comfort with Tencel
- Tencel T-shirts: ultra-soft, antibacterial and comfortable in every situation
- Tencel trunks: understanding the full lifecycle from wood to underwear
For now, the main thing to remember is that Tencel is probably one of the coolest fabrics you can wear every day, including for underwear.
Silk: luxurious, cool and a little delicate
Silk is naturally thermoregulating, lightweight and breathable. When it comes to feeling cool against the skin, it’s difficult to beat. The downside? It is delicate and requires careful maintenance, while its price tends to make it more suitable for specific uses than everyday basics. It certainly won’t make you feel hot, but it isn’t a practical daily option for everyone.
Bamboo: somewhere between the promise and the reality
Bamboo has had its moment in the sustainable fashion spotlight. Soft, absorbent and frequently presented as something of a miracle fibre. The reality is more nuanced. Clothing marketed as "bamboo" is almost always bamboo viscose, made using a fairly intensive chemical transformation process that removes much of the environmental advantage associated with the original plant. In terms of temperature regulation, bamboo viscose performs reasonably well: it’s relatively cool and soft. But beware of greenwashing. "Bamboo" does not automatically mean "sustainable".
Merino wool: summer’s most misunderstood fibre
We can already see the raised eyebrows. Wool in summer? Yes, provided we’re talking about fine merino wool at a low fabric weight. It is an exceptionally thermoregulating, odour-resistant fibre that can absorb up to 35% of its own weight in moisture without feeling wet. There’s a reason cyclists and hikers wear it in summer.
That said, for most people dealing with an urban heatwave, it still requires a bit of convincing. It probably isn’t the first fabric you’ll instinctively reach for when all you want is to feel cool.
What you should avoid when the temperature rises
Polyester and acrylic: the nightmare duo
To answer the question everyone asks: yes, 100% polyester can make you feel hot. Very hot. Synthetic fibres such as polyester and acrylic have a very low capacity for absorbing moisture (they tend to repel it rather than absorb it), which can create a greenhouse effect between the fabric and your skin. The result: trapped sweat, stronger odours and plenty of discomfort.
There are technical polyester fabrics specifically engineered for sport, with moisture-wicking treatments that perform much better. But standard polyester, the kind found in huge amounts of fast-fashion clothing, is probably one of the worst choices you can make in very hot weather.
Conventional viscose: summer’s false friend
One clarification is important here: "viscose" is actually a broad term associated with man-made cellulosic fibres produced from wood pulp such as beech, eucalyptus, birch or bamboo. Tencel, which we discussed above, is also a man-made cellulosic fibre, but its manufacturing process is very different.
- Conventional viscose is manufactured using several chemicals, including carbon disulphide, in a process that can be more polluting and whose environmental impact varies considerably.
- Tencel (or lyocell), on the other hand, is produced using a non-toxic solvent called NMMO, more than 99% of which is recovered in a closed-loop system, making the process significantly cleaner.
That difference in manufacturing also affects the quality of the finished fabric. Conventional viscose has moderate strength, particularly when wet, and tends to wear out more quickly. Tencel, by contrast, remains strong when damp and performs much better over time. That also helps explain why conventional viscose is cheaper: it costs less to manufacture, but compromises on durability.
And conventional viscose is precisely where the problem starts in summer. It’s lightweight, fluid and often marketed as a cool alternative to cotton. In the shop, it can certainly feel perfect for hot weather. But after a few hours in high temperatures, the problem becomes obvious: conventional viscose sticks to your skin as soon as you start sweating. It absorbs moisture, yes, but doesn’t move it away effectively and can end up feeling heavy, cold and plastered against your body. Not particularly pleasant.
Tight fits: a problem whatever the fabric
One final point that often gets overlooked: an overly tight fit can cancel out some of a fabric’s breathable properties if air can’t circulate between the garment and your skin, regardless of the fibre. Even the most breathable linen in the world will struggle to keep you cool if it’s skin-tight. A relaxed or straight fit gives air room to circulate and allows body heat to escape.
How each fabric compares for breathability and moisture management
As we mentioned at the beginning of this article, choosing a fabric that keeps you cool isn’t just about breathability. Its ability to manage and move moisture away from your skin matters just as much, if not more.
| Fabric | Breathable | Moisture-wicking |
|---|---|---|
| Bamboo | Yes | Yes |
| Cotton | Yes | No |
| Linen | Yes | No |
| Merino wool | Yes | Yes |
| Tencel | Yes | Yes |
| Polyamide | Yes | Yes |
| Polyester | No | Yes |
| Silk | Yes | Yes |
What you wear underneath matters too
Why underwear is one of the most important summer layers
We spend plenty of time thinking about the clothes everyone can see and sometimes forget the most important layer of all: the one directly against your skin. Wear trunks or briefs made from the wrong fabric in the middle of summer and you’re asking for sweat, constant discomfort and potentially irritation. Especially around the thighs (a problem plenty of people know well, and one we’ve covered in detail in our guide to preventing thigh chafing). The fabric you choose for your underwear can genuinely change how comfortable you feel all day.
Organic cotton vs Tencel: which is better for underwear?
Both are excellent options and in a completely different league from polyester or conventional viscose. But if we compare them fairly:
- GOTS-certified organic cotton is soft, natural and hypoallergenic. In normal conditions, it’s a fabric that won’t make you feel excessively hot. It’s familiar, easy to care for and a reliable choice.
- But Tencel goes further on almost every thermal and hygiene-related criterion: it’s lighter, cooler, dries faster after washing and naturally helps control odours.
Our Tencel trunks and briefs, just like our organic cotton underwear, are designed around these two different preferences. One is for people who prefer the familiarity of a natural classic; the other is for those looking for maximum everyday cooling performance.
And for T-shirts: sweat, odours and sweat marks
The same principle applies to the layer on top. In summer, a lightweight organic cotton or Tencel T-shirt can make a genuine difference compared with heavyweight cotton or, worse, polyester. We’ve explained how to choose a T-shirt that helps manage sweat, odours and sweat marks in a dedicated article. Fabric plays a central role, but it isn’t the only factor.
Cooler, more responsible fabrics: a combination that makes sense
There’s some good news here: many of the best materials for keeping cool are also among the more responsible options. Linen, merino wool and Tencel sourced from FSC-certified forests are fibres that can be better choices for the environment, workers and your skin (although this should always be assessed on a case-by-case basis). Polyester and other synthetics that can leave you sweltering in summer, by contrast, are also associated with highly polluting production processes and often shorter garment lifespans.
So be wary of "eco-friendly" synthetics promising both cooling performance and sustainability. Chemical "cooling" treatments applied to polyester fibres gradually wear away through repeated washing. The fibre itself isn’t inherently designed to keep you cool; it’s a surface treatment with an expiry date.
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When it’s hot, the natural instinct is to look for something "lightweight". But lightweight doesn’t automatically mean cool. What really matters is whether the fabric allows air to circulate and can manage perspiration effectively.
- Choose: linen, lightweight cotton (preferably organic) and especially Tencel if you’re looking for the best combination of cooling performance, comfort and sustainability.
- Avoid: polyester, acrylic and conventional viscose.
And if there’s only one thing you take away from this article, start with your underwear. That’s the layer where comfort really begins. Explore our organic cotton and Tencel collections, because a comfortable summer starts with getting the basics right.