Beginner's Guide to Base Layers
Base Layers (sometimes referred to as thermals) are the foundation of the layering system, and we believe, the most important layer to get right. You can have the world's most expensive Gore-Tex jacket, but wear a cotton t-shirt underneath and you may as well be wearing a bin-bag for all the benefit you'll feel.
There is a bewildering variety of men's and women's base layers available on the market today, suitable for all activities and weather conditions from Arctic exploration, to running in the Desert (which is why we don't call them the generic 'thermals').
In this guide we'll look over the main types of base layer, and some of the things you may wish to think about when purchasing.
What does a Base Layer do?
Worn next to the skin, a Base Layer is designed to fulfil two main functions.
- They are designed to remove moisture (sweat!) from your skin to aid your body's natural cooling process, which is called 'wicking'.
- They are designed to trap air next to the skin to provide insulation (remember, it's your body warming trapped air that keeps you warm, not the fibres themselves.)
In the most basic terms this means that when you're working hard, your base layer is removing sweat from your skin cooling you down, and when you're cool (and therefore not sweating) the trapped air is keeping you warm. The other benefit is that if you've been working hard and then stop for a brew, there's little to no moisture on your skin, which prevents a sudden chill effect...if you've experienced it, it's is rather unpleasant!
Now obviously depending on your activity and/or the weather conditions, you may need a base layer that favours one or the other of these functions. This is why there's such an array of choice. (Image to right shows Polartec Power Dry fabric)
Base Layer: Fabrics
At the most basic level, there are two types of base layer fabrics; synthetic and natural. There is a lot of technical stuff (which I find fascinating) which gives each its properties, however for a beginner's guide the following summary covers the main points.
Synthetic Base Layers
- Made from: Polyester, polypropelene etc.
- Generally inexpensive.
- Easy care.
- Excellent wicking and drying times.
- Good insulation.
- Fibres do not 'breathe', only space between them does. (When very warm can feel a bit uncomfortable)
- Can smell pretty bad after a day or two!
Top Brands Helly Hansen | Berghaus | Under Armour
Natural (Merino Wool) Base Layers
- Made from: Merino Wool.
- Quite expensive.
- Generally heavier than synthetics.
- Easy care.
- Very good wicking and drying times.
- Excellent insulation.
- Excellent breathability, fibres themselves breathe (feels more 'natural' than synthetics, copes better with a range of temperatures).
- Do not retain odour.
Top Brands Icebreaker | Smartwool
In practical terms synthetics are an ideal workhorse, providing a great balance between performance, comfort and price. They dry much faster, can easily be washed and dried when camping or travelling, provide good insulation depending on weight and won't break the bank.
Merino base layers are arguably more comfortable, with the actual fibres themselves breathing and absorbing water, however once they become saturated they will take much longer to dry and are heavier. For many the extra cost will outweigh the benefits.
Manufacturers will argue all day about which is the 'best', however I have used both extensively and overall I slightly prefer merino, BUT more often than not you'll find me in a Helly. If you can, try one of each and see which you prefer, or ask around for personal opinions! Generally speaking though, for cold weather merino will be ideal!
Base Layers Styles and Features
So we've made the choice between synthetic and merino, now we need to work out which of the many styles and features we need
Loose or Close Fit?
>> For warm weather, travel or high aerobic activities like running or cycling, it is often best to chose a loose fit base layer. This traps less air and therefore doesn't warm you so much, acting more like a 'T-Shirt' than a thermal. It will also have less fabric in contact under the arms or across the shoulders which often makes it comfier to wear.
>> For all year round use in a wide range of activities a 'close' fit is ideal. The Helly Hansen Lifa Dry T-Shirt and Lifa Dry LS Crew are probably the most famous and recognised of this type and are my utility base layer for most activities. The majority of base layers are designed to be quite tight, but not restrictive...basically you want it in contact all over, but not so much that it's uncomfortable.
This provides the optimum balance of wicking and insulation, which both work best when fabric is against the skin.
>> For cold weather use or static activities where warmth is paramount, you want a close fit base layer, but thicker! Merino is usually the best choice, however there are some hybrids which use both fabrics to give you the benefit of both worlds. (These can be very warm, so not great for summer trekking!)
Long or Short Sleeve?
Long sleeve base layers will provide much more warmth, but at the cost of some ventilation. Short Sleeve are much cooler.
Zip or Crew Neck?
Zip neck base layers allow for extra ventilation, which is ideal when working hard, or the stop/start routine of a day on the hill. You can ditch a surprising amount of heat from your torso very fast, and when you're cool again, zip up and the heat returns almost instantly.
Zip necks are generally more expensive however and some people do not like the extra fabric which will be present around your neck. (They can also be quite annoying if you have a beard)
Crew necks are great for when you expect similar conditions all day (running, cycling, gentle walks), and they will often feel more 'natural' to wear, especially under many layers.
Many of the more technical base layers have thumb loops. These are ideal for activities where upper body movement is essential (cold weather climbing, cycling, skiing) as they stop the sleeves riding up and help prevent drafts. For warm weather use however they will cut down on ventilation, and can feel more restrictive. Thumb loops are usually present on base layers designed for the sports/conditions where they'd be useful.
Often people complain that their expensive waterproof jacket is leaking. More often than not it turns out that the problem is that they have been wearing a cotton t-shirt as a base layer.
Unlike merino wool or synthetics, which will steadily release moisture through the layers, cotton loves to hold on it. As a practical example, take a synthetic t-shirt and a cotton one out of the washing machine and feel the difference in weight...then see which one dries first!
In real life this means that all your sweat is stuck against your skin, which is uncomfortable in normal circumstances. In extreme circumstances once you stop working your body will cool very rapidly (water conducts heat around 20 times faster than air) and you will notice that you begin to feel cold within seconds. In very cold weather this rapid drop in temperature can lead to a rather unpleasant experience, or worst case, hypothermia.
Cotton t-shirts are often worn travelling, but for outdoor applications, you'd almost be better off naked!
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