August 19, 2021

How To Choose From Our Range of Thermal Underwear

We’ve got a range of fabrics and weights so you can choose just the right garment for your use case.

The Role of Thermal Underwear

Thermals form the foundation of your microclimate by trapping a fine layer of air right against your skin. Thermals also wick moisture away from your skin which keeps you comfortable. Without thermals, your layering system won’t hold on to your microclimate as effectively and your expensive Gore-Tex jacket won’t be able to expel your sweat as effectively.

Merino or Synthetic?

Merino is all the rage at the moment and for good reason. The natural anti-bacterial properties of wool make it ideal for wearing against the skin. It will feel comfortable and won’t smell even after weeks of wear. Merino is much finer than normal, scratchy wool but some people will still be sensitive to that prickly feeling.

While Merino wool normally has a fibre thickness of between 17-24 microns, Montbell’s synthetic Zeo-Line fibre is less than one micron. This has a couple of advantages. First even the most sensitive skinned person will find this soft and smooth on the skin, secondly, these finer fibres wick moisture more effectively keeping your skin drier in wet conditions and lastly, more air can be trapped for less weight. If you are looking for the warmest thermals possible, synthetic is the way to go.

Synthetic will also out perform Merino in the wet. When it comes to drying times and moisture wicking performance, synthetic beats wool everytime.

Lightweight or Middleweight?

Nobody likes being cold so it’s common to assume that you should buy the warmest thermals possible but you should be looking to maintain a comfortable temperature with a series of layers. The base layer is important for comfort and for it’s moisture wicking properties, it’s also the most difficult layer to take off! It’s safe to say that in alpine conditions it’s sensible to go for a thicker, warmer thermal.

Outside of the mountains, unless you’re a real cold fish, a lighter thermal will give you more versatility in your layering system. This becomes really important when you’re hauling your pack uphill in the rain. You’ve stripped back all your layers but you still need to keep your base layer on, inside your waterproof shell to maximise its breathability. If your thermal is too warm, you’ll be unable to maintain a comfortable micro climate.