Gear Insights: How to choose a base layer

When it comes to comfort when walking, there are few things more essential that what we put next to our skin. Called 'base layers' by outdoor shops and also just known as 'shirts' by normal people, this layer has an important role in keeping you warm and in wicking away the moisture you generate during exercise. There are a number of different materials to choose from, which have other attributes discussed here.

There's no point spending hundreds of pounds on an excellent waterproof jacket for its breathability if you're going to go for a baselayer which doesn't perform well and prevents all that moisture from being transferred to the jacket to be wicked out.

Why not just a normal T-shirt?

Most people have a lot of T shirts, and you'll often see walkers out in the hills wearing something you might wear down to the pub. Most T shirts are made of cotton, which is possibly the worst fabric to wear when exercising. It holds moisture, so is easily soaked when you sweat and will take ages to dry if it gets wet in the rain. It also loses it's thermal abilities when wet, so you'll lose even the small amount of insulation it provides. This is also the reason we advise against wearing jeans when walking (which are made of cotton) as they actually make you colder when wet, transferring heat away from your body.

So what other materials are there?

The two most common fabrics that base layers are made from are the synthetic polyester and the natural Merino wool. Merino wool comes from sheep in New Zealand and is much softer on the skin that other woollen products; it's great at keeping the heat in and still keeps you warm when it's wet. It also has anti-microbial properties which stop the build-up of the bacteria that cause sweat to smell, meaning you can happily wear it for several days in a row.

Polyester on the other hand is great at wicking away the moisture produced by exercise, dries quickly, and is cheaper than Merino. In general, if you're being active I would suggest polyester, but for long days out in cold weather, or if you're on a social walk and may have to wait around for other people or just like to stand around talking, then go for Merino. Several companies produce base layers that blend these two fabrics, so if you're unsure of where you sit on the outdoors scale and want one top for everything, perhaps opt for a blend.

Another material that is being used more and more in base layers is bamboo, which has a very soft feel and which is theoretically more sustainable than the other fabrics.

What about thickness?

As well as the material, there are other features of base layers which make them suited for different conditions. A thicker material will in general be warmer, and most companies have developed their own scale to guide you through the different thicknesses of their products and what conditions they are best suited for. Some polyester base layers will also have mesh sections, particularly on the back, to help with the cooling process if you're walking fast with a backpack.

Whatever you end up choosing, remember to clean base layers regularly to remove any sweat build-up and keep the fibres clean.