Choosing The Best Thermals For Your Activity

We all know that rule number one of building an outdoor wardrobe is effective layering. It’s easy to get distracted with colourful shells and trendy down jackets, but an effective outdoor layering system has to start with the foundation. A well-performing thermal base layer is key to keeping ourselves warm and comfortable in the outdoors, but the type of baselayer you need will likely vary depending on a number of factors, including activity and conditions. We’ve compiled a summary of the best thermals for hiking, camping, snow, and extreme cold to help you choose the right thermal baselayer for your next adventure.

What Are Thermals?

Thermals, or base layers, are garments that are specifically designed to be worn next-to-skin and layered underneath all other items of clothing. The purpose of a thermal base layer is to regulate body temperature and keep you warm, by providing a layer of insulation and wicking sweat away from the skin so that you don’t feel cold.

Materials

Baselayers should be sweat-wicking to keep you comfortable during high-output activities and warm conditions, with the ability to stay warm when wet and prevent chill in cold conditions. This means that thermals are most commonly made with fabrics like merino wool and synthetics, or a blend of the two. Steer clear of cotton when choosing a baselayer – it is slow-drying and will almost always make you feel cold and uncomfortable, especially when you’re working up a sweat.

Merino wool is an insulating and moisture-wicking fabric that has natural odour resistance. Merino can take a while to dry (although it dries much faster than cotton), but it also stays warm when it is wet, which makes it a great option for both hot and cold climates. 

Synthetic materials are usually lighter in weight and faster drying, so they perform better in warmer conditions. However, synthetics can often build up a smell as they lack odour resistance, and they will not retain warmth if they get wet (read more about the comparison between merino wool and synthetic materials here).

Weight & Warmth

When it comes to weight, thermal fabrics are usually measured in grams per square metre (GSM), giving you an indication of how warm the garment is. Midweight base layers usually sit at around the 150-250 GSM mark – anything less is considered lightweight and anything higher is extremely heavy.

Style & Fit

Common thermal styles include long and short sleeved tops and leggings, as well as thermal underwear. Thermals should always fit snugly in order to trap heat and effectively draw moisture away from the skin for optimal performance. You may also want to consider a base layer with a zip, which will help you better adapt to changing temperatures and output levels.

Best Thermals For Hiking

Choosing thermals for hiking depends on a few different factors, most importantly the external environment and the length of your trip. 

If you are heading out in the height of summer, a super lightweight synthetic base layer might be your best choice. However, when facing mixed or cooler conditions, opt for a medium-weight merino wool thermal that will keep you warmer and will perform well in a range of conditions.

If you are embarking on a multiday hike where you don’t have access to washing facilities, merino wool is the better option as it suits all temperatures and is naturally odour resistant. However, for shorter day hikes, synthetic base layers work great for quick-drying comfort on the move.

There are a range of thermals available that blend merino with synthetics to combine the benefits of both materials for warmth, breathability, and durability.

Remember to avoid cotton when hiking. Cotton retains moisture, is slow to dry, and stays cold when wet. This can get pretty uncomfortable and possibly dangerous during a sweaty hike as it prevents you from staying warm.

Best Thermals For Camping

Thermals are great for camping because they provide an extra layer of warmth and help maximise the temperature range of your sleep system. 

We’d always recommend merino wool as a camping base layer because of its odour resistant and insulating properties. Synthetic materials are likely to build up a smell if slept in, and will not be the most comfortable next to the skin.

Weight and style will depend largely on season and temperature. Opt for lighter weight, short-sleeved items in the summer, and heavier, long-sleeved garments in the winter. Check out some more tips for keeping warm on winter camping trips here.

Best Thermals For Snow

Choosing the best thermals for snow will depend on your activity and output levels. If we sweat too much, moisture build up can cause core body temperature to drop drastically in colder conditions – so the aim is to stay warm without overheating.

For stop-start activities like resort skiing and mountaineering, opt for a base layer that is going to keep you warm when you are stationary but will wick sweat on the move. A light-mid weight merino thermal should do the trick, and it might be worth considering a zip-neck to help trap and expel heat quickly. 

For higher intensity activities like ski touring, lighter weight will work better to prevent moisture build up. Synthetic materials are great because they typically dry faster than merino. Alternatively, thermals with zone mapping technology, such as Icebreaker’s ZoneKnit, can work to effectively regulate your body temperature using a combination of warmth and ventilation.

Whatever you do, do not wear cotton during snow-based activities as it absorbs moisture and dries slowly, which could cause body temperature to drop dangerously in snowy conditions.

Best Thermal Clothing For Extreme Cold

When it comes to the best thermals for extreme cold conditions – warmth is absolutely key. The best fabric for both warmth and insulation is undoubtedly merino wool. 

If you will be mainly stationary then a heavyweight merino wool fabric will keep you toasty all day long. If you’re planning to move around a bit, then reduce the weight as much as you can without sacrificing warmth to avoid excessive sweating which could lead to a drop in body temperature. 

You’ll want to opt for long sleeves and potentially extra layers depending on how cold the climate is. Check out our blog for some more tips on how to gear up for winter.

Choosing the right thermals will depend on your activity and environment. Browse Paddy’s range of thermals and baselayers for all types of adventure.