How to Choose Base Layers for the Outdoors

Base Layers are the most important pieces of clothing you can wear. Base Layers are the ones which separate your sensitive skin from the elements and your other clothing – whether that be regular underwear or something more specialised for higher intensity activities and extreme weather.

Our quick guide aims to show the Pros and Cons of different types of Base Layer, and how to match them to your activity.

Smartwool NTS Micro 150 – A simple merino layer


A Good Fit

Whichever material you opt for, a good Base Layer should be snug, and flexible to move with your skin during activity. You need a close-fit; for cold-weather Base Layers so that they trap an insulating air-layer around you, and during hot-weather so that they wick away your sweat properly. Wearing base-layers will make you warmer than bare skin, but they will serve to manage that excess warmth and sweat well.







Smartwool PhD NTS Light - A windproof front panel
Smartwool PhD NTS Light – A windproof front panel

Panels and Sections

Different areas of the body operate at different temperatures, and a good Base Layer will be comprised of different sections or materials to manage that. Your armpits and groin will be really warm all year round, but your chest and thighs (for example) will be subjected to cool winds more, and thus be cooler.

Look for a Base Layer which uses panels in the right places for the activity you’ll be doing.






Smartwool Mid250 Funnel Zip - Thicker, high-neck, long sleeves
Smartwool Mid250 Funnel Zip – Thicker, high-neck, long sleeves



Thermal Base Layers

Thermal Base Layers all operate by trapping a layer of air next to your skin which then acts as a buffer between you and the cold air outside the garment. Different Base Layers do this in different ways, but the principle of that air-layer is the same in any garment. All Base Layers will work best when teamed with a good mid-layer in winter, and some brands actively specify a ‘system’ of garments which helps this. A good thermal will usually have some kind of ‘loft’ (thickness) to it. Extremely technical Base Layers may mix loft and channels to balance that trapped air and sweat management.





Smartwool NTS Micro 150 - Lightweight summer wear
Smartwool NTS Micro 150 – Lightweight summer wear

Summer Base Layers

The job of a summer Base Layer is to protect you from the sun, and wick away sweat so it evaporates as quickly as possible. They will typically be quite thin and not have much loft. Summer garments will sometimes have an anti-microbial treatment to avoid them smelling too bad, or be made from a naturally less-pongy material, i.e. one that limits bacterial growth in its fibres.







Merino Wool Base Layers

Our favourite all-rounder at GearWeAre, Merino Wool is soft to the touch and performs well as a wicking fabric. It’s not quite as quick to wick away sweat as a synthetic fibre, but will deal with anything except extreme sweating with relative ease. Merino wool Base Layers make for excellent travel and expedition layers because they will resist bacterial growth for a fairly long time, and stay stink-free for days on end.

A 3 year old Smartwool top – much used

Synthetic Base Layers

Man-made, solid fibres won’t absorb much moisture at all, and will be the fastest wicking of all Base Layers. In extreme sports, they’ll generally perform the best. But, they’ll generally start to smell fairly quickly and need washing with a specialist wash to get rid of bacteria which are tucked in between the tight fibres, breeding merrily. Synthetics, to our mind, have the least appealing ‘feel’ of all Base Layers, but that’s a personal preference.

Blend fabrics

Blends of wool and synthetic or other natural materials like bamboo and synthetic can often help create a good all-round Base Layer. The natural materials bring their inherent softness and performance, and the synthetics help to create a lasting structure (shape) and encourage fast wicking.

Smartwool PhD Run Divide – A mixed fabric garment

Cotton Kills

An old saying which is used to indicate that cotton – the favourite material for casual clothing – absorbs sweat, rain and other moisture and then uses lots of your body’s energy to try to evaporate that moisture from the individual fibres. It takes so much energy to dry out cotton that you can chill your skin and end up getting hypothermia. Cotton also serves as a nice breeding ground for bacteria to munch on your sweat, so it will get smelly quickly. But, let’s not be completely anti-cotton. It has its uses as a soft, comfortable material for warmer climes.

Girls vs Boys

Apparently, men and women are different. Who knew!? In winter, women will require more insulation, and should consider layering to maximise this. 2-3 thin layers will be much better than 1 thick one. And, of course, women will need structural support of some kind in a next-to-skin Base Layer, which is designed to be worn instead of a bra in some cases. This will, unfortunately, be at the expense of wicking and coolness, but a good support bra/top will be seamless and well-fitted to avoid chafing during activity.

Smartwool PhD Seamless Racerback Bra

Cleaning Base Layers

Generally, Base Layers should be washed on a 30-40C cycle, with specialist soaps or proprietary washes like Nikwax’s Base Wash. Really sweaty and smelly synthetic Base Layers can be treated to a hotter wash, but wool and blend fabric shouldn’t get too hot. They should all be air-dried naturally to ensure that they keep their close-fitting shape.

And lastly… Design

There are some important design features in many base-layers which perform a function, as well as add to the look. A neck zipper will be easier to put over your head than a tight neck, and allow you to vent easily. Seamless shoulders will prevent a backpack rubbing. Thumb loops will keep your sleeves down, and the back of your hands warmer in winter. And you may even see Base Layers with small pockets when they’re designed to be worn as an ‘only layer’ – usually in summer.



This guide has been sponsored by Smartwool. For more information on Smartwool’s range of Merino and Blend Base Layers (and more) take a look at their site, here.
  • thanks for making this really easy to understand. I was confused before, and didn’t know where to start with the shopping!

    I am waiting for a merino wool layer to turn up in the post, and glad I made a good choice.

    Definitely looking at getting a few different base layers – the Smartwool Mid250 Funnel Zip looks very very nice.