Base Layers – Thermal Underwear

Base Layers: What are base layers, and how do you wear them?
Thermal Underwear: What is thermal underwear? Are base layers thermal underwear?
Confused about the different materials used in base layers/thermal underwear?

We will answer these questions in this article:

Sorry, but First We Need to Talk about Sweat

Sweat glands are found throughout the body and are responsible for secreting the watery, salty perspiration that is most commonly caused by high body temperatures. Sweating causes a decrease in core temperature through evaporative cooling at the skin surface.

People have an average of two to four million sweat glands. The volume of water lost in sweat daily is highly variable, ranging from 100 to 8,000 mL/day. During average-intensity exercise, sweat losses can average up to 2 litres of water/hour.

What are Base Layers?

What are base layers, and what has sweating got to do with anything?

Base layers are thermal underwear that are designed to be worn next to your skin. Their key purpose is to move perspiration from your skin into the fabric, through its fibres and onto the fabric’s surface, where it can evaporate. This is known as ‘wicking’. Because your skin remains dry, you feel less cold and more comfortable.

Base layers also trap a layer of warm air between your skin and the base layer, which acts as insulation.

How to Wear Base Layers

Getting the Correct Fit for Your Base Layers

In order to keep your body dry, base layers should closely follow the contours of your body, ensuring that much of your skin has a wicking layer next to it. Lightweight, snug-fitting (but not over-tight) base layers are the best at doing this. Base layers should have a degree of stretchiness, ensuring that your movement is not restricted.

Although you can buy base layers with a baggier fit, they are not as effective at wicking away moisture from your body.

In advertisements, snug-fitting base layers are often worn by models with the body of an Adonis. For the rest of us, wearing such snug-fitting garments can make us feel a little self-conscious. However, these garments are typically hidden from view and worn underneath another layer (the mid-layer). Snug-fitting base layers work best.

Sizing

Check the manufacturer’s size guides to ensure that you get the best fit.

Length

A longer shirt will prevent gaping when bending over and sitting down, preventing you from losing body heat.

Base Layers: Styles and Features Worth Thinking About

One-Piece or Two-Piece Base Layer?

Base layers are available in one- and two-piece options. The one-piece base layer, being a single garment, might be considered to be warmer as there are no gaps created when moving around. However, going to the toilet can be awkward. Some of the one-piece base layers have a flap at the back (with buttons or a zip). Alternatively, you might need to strip down to use the loo, which is never ideal.

You don’t have these problems when wearing a two-piece base layer.

Advantages of Two-Piece Base Layers

Two piece base layers are more versitile. Often, you are able to buy the upper and lower garments seperately, in order to suit your body type. You can combine different weight base layers, for example wearing a more lightweight (or no base layer) under your trousers.

You can wear different style tops, which suit your activity or preference (e.g. wearing a top with an inclusive hood or a with a zip). Thereby, providing flexibility.