Ski Walking

Base Layers Explained

When planning any outdoor activity, you must always ensure that you have the correct clothing to facilitate what you have planned for that day and the potential weather conditions you may face. In the UK, the weather can change multiple times throughout the day, which is why packing various layers of clothing is important.

As the weather heats up or cools down you can remove layers to suit, and the first thing you should consider is always the base layer. For more information on layering, check out our Winter Layering Guide.

What is Base Layer Clothing?

A base layer is the layer closest to your skin and should act as a constant ‘second skin’ throughout your day. Base layers provide a layer of warmth while absorbing and evaporating your sweat to keep you feeling warm and comfortable.

Base layers are versatile pieces of clothing which come in different fabrics and styles that have benefits best suited to certain climates and conditions. In this base layer guide, we will explore the attributes of different base layer types and what makes them special as well as helping you to choose the best base layer for your circumstances.

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How Should Base Layers Fit?

When trying on a base layer you should ensure that it feels tight against your skin whilst still giving you the flexibility to move. Although base layers should fit tight against your skin, don’t be tempted to buy a size smaller than your normal dress size (especially if buying online). If you’re not sure what sized base layer you should purchase, bear in mind that we design our garments with the intention that they will be tight fitting.

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What Does Wicking Mean and Why Is Wicking Important?

The definition of the word wicking means to move moisture from the inside to the surface, which is exactly what wicking fabric does. It literally wicks away sweat and moisture from the body, keeping your skin dry.

It is important to have wicking fabric in sports clothing as you produce more sweat than usual. If this is left wet against your skin it will begin to cool you down, give you a chill and make the fabric chaff your skin.

All of our base layer garments are produced with wicking fabric, but some materials are more effective at wicking than others.

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What Fabrics Are Base Layers Made From?

Our base layer clothing comes in two different types of fabrics: synthetic and merino wool. We also, on occasion, use DuoSkin® technology to enhance the breathability of the garment. Let’s explore the benefits of each and in what circumstances you would choose one over the other.


Synthetic fabrics are generally the cheapest of all base layer garments. These base layers are quick-drying and high wicking which makes them perfect for high exertion activities. They are also lightweight and flexible, making them suitable for sports activities such as cycling or anything where your body is constantly moving.

However, synthetic fabrics are not naturally antibacterial (unless otherwise specified), meaning they will retain the odour from sweat. They are also not as warm as merino wool fabrics, which makes them more suited to milder climates.

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Merino Wool

Merino wool is the warmest of all our base layer fabrics. Merino wool is directly sourced from merino sheep, giving it the natural ability to regulate body temperature and in turn, keeping you nice and warm but prevents you from overheating. In the wool, there are small air pockets that draw excess heat away from the body while retaining heat within the fibres to keep you comfortable, no matter what the weather.

Merino wool is also naturally antibacterial, meaning it won’t retain the smell of body odour in the fabric, and also has natural UV protection. The wool fibres are non-abrasive and suitable for people with sensitive skin.

The only downfalls of merino wool, however, is that it takes longer to dry and can be more expensive than synthetic fabrics (you pay for what you get) and can prove to be less effective at wicking sweat away from the body than synthetic.

We’ve created an Expert Advice guide to Merino Wool that offers more information on what the material is as well as its benefits.

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Another fabric that we use in our base layers is DuoSkin® intelligent fabric, which is an added benefit of our synthetic range. DuoSkin effectively draws moisture away from the skin which then quickly evaporates when brought to the surface of the fabric, leaving you dry and comfortable. Its tightly woven fibres are high wicking and quick-drying, making them a fantastic choice for activewear.

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Our Trespass Performance (TP) Rating Explained

Each of our base layers come with a TP (Trespass Performance) rating. This uses a three-tier system that splits our diverse base layer range into three simple categories for ease of reference. These categories are TP50, TP75, TP100, and demonstrate the general percentage rating of the technicalities and performance these garments offer.

If you would like to learn more about the difference between our TP ratings then please read our Trespass TP Ratings Guide. You can also filter by TP rating on the left-hand side of our base layer page.

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Can Base Layers Be Waterproof?

The main purpose that base layers have is to trap in body heat and wick sweat and moisture away from your skin, which is why base layers are not traditionally waterproof.

Base layers are designed to be lightweight and worn in conjunction with additional layers, so if you’re looking for waterproof protection to go alongside your base layers, we’d recommend investing in additional waterproof layers – such as a waterproof jacket or waterproofs for men and women.

If you’re looking for more Expert Advice on how best to layer your clothing, check out our Guide to Winter Layering. We’ve also created an Expert Advice Guide to Waterproof Jackets if you require assistance in choosing the best waterproof jacket to suit your needs.

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What Are the Different Styles of Base Layer?

Base layers come in a variety of styles and cuts including long-sleeved, short-sleeved, bottoms and vests. These different styles all come with their own benefits and suitability.


If you’re looking to wear your base layers in summer or in warmer climates, our short-sleeved and sleeveless options may be more suitable for your activities. Vest-style base layers will typically be the coolest option, followed by short-sleeved then long-sleeved. What you choose depends mainly on personal preference and what weather conditions you may be facing.

Winter base layers are typically long-sleeved but this all depends on how adaptable you require your base layer to be. Consider what you will be wearing on top of your base layer before deciding what style to purchase. Does your mid-layer, fleece or jacket come with arm warmers? This factor may make you choose a shorter-sleeved base layer for use in the winter months. Don’t forget that longer sleeves will ultimately keep you warmer and protected from the chill as they keep blood flowing to your forearms and then onto your hands.

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Base layer bottoms are great for adding an extra layer of warmth while you are enjoying the outdoors, but they are also extremely versatile. Designed to insulate body heat and eradicate the moisture produced by your body, base layer bottoms are perfect for extreme snowsports, cycling, hill walking and even for under your normal day-to-day outfit on extra cold days. Wear them on their own, underneath shorts or as a base layer underneath ski trousers or waterproofs.

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Common Uses

Base layers can be incorporated into your outfit for a wide range of activities. Skiing is the most obvious one, as you’ll need an extra layer to beat the harsh, cold air on the mountain and control your body temperature. They also make a great addition to walking clothes on colder days, or for wearing under shorts when running or cycling, to offer warmth without additional baggy material.

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Whatever you use a trespass base layer, such as merino wool thermals, for, you’ll find them an excellent addition to your outdoor garb and you’ll be surprised how much extra warmth can be supplied from such a thin layer of material.