Polartec Delta – the cooling base layer fabric

Base layers are an oft overlooked but important item of hiking apparel. However, not all base layers are equal, because not all fabrics used to make them are equal. When it comes to hot-weather wear, some are better than others, and Polartec’s Delta fabric is one of the best.

Man wearing Thrudark Polartec Delta t-shirt

by Ben Weeks |
Updated on

If you read any review for base layers in any magazine or on any website, there’s one word you can bet your bottom dollar will appear: wicking. If you’re already familiar with what wicking is and why it’s important (and if you’ve read many base layer reviews, you almost certainly will be) you can skip the next paragraph. Otherwise, read on…

What is wicking?

A fabric’s ability to wick refers to how well it moves moisture, usually sweat, away from your skin. For example, cotton is a terrible wicker. It absorbs moisture but holds onto it. Conversely, wool, particularly merino wool, is a pretty good wicker, rapidly moving perspiration away from your skin and allowing it to evaporate. But king of the wickers tends to be man-made fabrics. Made from synthetic fibres, these wick moisture away quickly and efficiently and dry faster than their natural counterparts. Why is this important? Well, clothing that’s saturated with moisture causes you to lose heat much faster, making it easy to go from hot and sweaty to cold and uncomfortable remarkably quickly - particularly on a windy day. Quick wicking fabrics don’t become saturated, preventing this from happening.


For over 40 years Polartec has been a maestro of outdoor fabrics, weaving the materials from which some of the best outdoor brands create their performance clothing. So it’s of little surprise that several created specifically for base layers sit in their fabric portfolio, all of which do a magnificent job of wicking and warming, depending what season you’ll be using it in.

But here’s a question: what if you don’t want your base layer to be too wicking? And here’s another question: why wouldn’t you want your base layer to be too wicking? To answer both those questions we need to take a closer look at a very special base layer fabric. It’s time to meet Polartec Delta.

Polartec Delta cooling fabric

Let’s talk about sweat. It’s important. It’s the body’s natural way of moderating its temperature and cooling itself down on hot days. But it isn’t the sweating itself that reduces your temperature, but rather the evaporation of it off your skin. But if that sweat is whisked away from your skin too quickly – say, by a highly wicking base layer fabric – it prevents your sweat from doing its job and will reduce the effectiveness of your body’s cooling system. It’ll keep you dry but won’t help you stay cool. This is where Polartec Delta comes in.

ThruDark Oryon Delta T-Shirt made with Polartec Delta fabric

The science

Delta is a cooling fabric that works differently to other Polartec base layer fabrics such as Power Dry or Power Grid. Rather than simply wicking moisture away as quickly as possible, Delta utilises our sweat the way nature intended. How? We’re glad you asked.

Polartec Delta is a ‘bicomponent’ knit. This means the fabric is made from two different fibres. In Delta's case it’s a mix of a synthetic polyester fibre and a natural lyocell fibre which have been knitted together to provide two different functions. But it’s the way these fibres and functions perform together that’s so clever.

Polartec Delta fabric

The natural lyocell fibre yarns, which are hydrophilic (water loving), absorb sweat and then distribute it around the fabric. Think of it like the coolant in a car’s radiator system. This distribution of moisture allows your skin to benefit from the effects of evaporative cooling as the sweat dries.

Evaporative cooling is the single biggest way our bodies shed excess heat when we're hot. It's the reason why we sweat. As our sweat evaporates, latent heat from the skin's surface is removed. This yields a reduction in temperature on the skin surface.

Of course, if left unchecked this would cause exactly the same problems that a cotton t-shirt would. The fabric would become saturated, causing ‘wet cling’. And while ‘wet cling’ might sound like a vaguely sexist 1970’s holiday park competition, when it comes to outdoor gear it’s a real problem.

Wet cling is when a fabric gets so saturated with moisture that it sticks to the body. It occurs when a fabric is at its maximum capacity for moisture uptake and cannot move moisture from inside to out quickly enough to keep the user dry.

Once the fabric is saturated you are no longer drying, and in the right (or wrong, depending how you look at it) conditions, this could cause your body temperature to drop very rapidly. But Polartec Delta is a mixture of two fibres remember? And controlling the spread of moisture is where the second one comes in.

The synthetic polyester fibre yarns are hydrophobic (water hating). They resist absorbing water, creating zones of dryness within the fabric to promote maximum breathability and a comfortable dry time. What’s more, the special knit structure uses raised touch points to eliminate wet cling. The yarns chosen also have a naturally cool touch so you won’t mind putting it on when the weather is hot.

66 degrees North Grettir Light T-shirt made with Polartec Delta fabric

But what about the smell?

It’s difficult to talk about sweating without talking about odour control. Traditionally, synthetic base layers had a tendency to smell after a few wears. Brands began to counteract this by using chemical treatments, often based on metals such as silver. But with sustainability increasingly under the microscope, the use of mined compounds is being frowned upon, and environmentally aware brands such as Polartec are looking to alternatives.

Fresh Face is a new bluesign certified anti-odour treatment from Polartec. Instead of using metals, it makes use of sustainably harvested mint oil extract. After hundreds of sniff tests – yes, Polartec got groups of people to wear the fabrics, get hot and sweaty in the fabrics, and then sniff the fabrics – they found that Fresh Face was just as effective as metal-based alternatives, if not more so. In fact, the only bad news is that the treatment is odour free, so you won’t be giving off minty wafts as you move.

Polartec Fresh Face odour treatment is made from natural mint oil

Polartec Delta – the summer-focused base layer fabric

While there is undoubtedly a place for quick wicking fabrics in base layers, when the heat is up and you’re working hard, these might not be the best choices to keep you cool. But thanks to Polartec Delta, there’s now one that will.
Visit polartec.com to learn more about their Delta fabric (along with their vast range of other types of fabrics) and discover which outdoor clothing brands are already using it in their products.


This breathable, half-zip t-shirt is the perfect antidote for arid conditions. Constructed from


The Polartec Delta fabric used in this T-shirt  is designed to be next to skin, featuring a


The Polartec Delta fabric used in this T-shirt  is designed to be next to skin, featuring a


Keeping you cool under the glorious summer sun. Made with Polartec Delta. The most beautiful time


Keeping you cool under the glorious summer sun. Made with Polartec Delta. The most beautiful time

Just so you know, whilst we may receive a commission or other compensation from the links on this website, we never allow this to influence product selections - read why you should trust us