By: Blonde Two

Fi Darby (Blonde Two) is an adventure and outdoor writer based in Devon. Fi specialises in walking routes, gear reviews and outdoor tips. The outdoor market is growing. Don’t ignore it. Get in touch with Fi today to find out more.

If you hibernated through January, now is the perfect time to turn your thoughts to getting outside again. Watch the weather though, especially the temperature. It’s still chilly out there, and it isn’t time to ditch the thermal base layers just yet. With lockdown limiting us all to limited, shorter ventures outdoors at the moment, the good news is that thermal leggings and tops are just as good at keeping you warm inside as they are outside. If you haven’t discovered the joys of this invisible clothing layer, we have some recommendations for you.

Thermals are for life

Once you’ve worn a pair of thermal leggings, or indeed a thermal base layer top, you won’t want to go back to single layer clothing. Whether you love walking, running, cycling, wild camping, or outdoor swimming, not only are modern-day thermals great at keeping you warm, and wicking away moisture from your skin during outdoor activity. They also do a pretty good job at saving on the heating bill whilst you are working from home.

Base layers for outdoor and indoor activities

The great news is that base layer tops and bottoms for outdoor (and indoor) life are far easier to buy than they used to be. They also come in a wide range of price brackets and fabrics. I always think if you can find clothes that do multiple jobs, you (and the environment) are on to a winner. Thermal tops and bottoms have to be top of the multi-use league tables. All you need to do is think outside the box (or wardrobe). Here are a few examples:

  • Bamboo leggings worn underneath a pair of jeans can save money on your heating bill
  • Merino thermals make great camping pyjamas but are also cosy on a chilly night at home
  • Black thermal leggings are far warmer under a skirt than a pair of tights
  • Watching movies or TV is far more comfortable in thermals than in any other type of clothing
  • Thermal base layers don’t take up much space in your rucksack but can add emergency warmth
  • With careful colour coordination, you can wear a thermal top under a smart blouse for online meetings
  • Buy a pair of leggings for morning yoga then layer up over them to keep warm all-day

Save money on your heating bill

I could go on but hopefully, I’ve convinced you by now of the value of thermal clothing. I can honestly say there isn’t a day between November and May that doesn’t see me reaching for some form of base layer top. If I don’t put one on in the morning, I will usually be wearing one by lunchtime. This means I’ve had the opportunity to try out different fabrics and makes in all kinds of outdoor and indoor situations. From cheap and cheerful merino leggings to higher-end tops, I love my thermals and would recommend them as the ultimate outdoor/indoor gear option.

Synthetic, merino or bamboo base layers?

Because we Blondes are so helpful (but also because we love outdoor gear and staying warm), we’ve taken the time below to explain the advantages and disadvantages of three different types of thermal base layers. We’ve come a long way from the days of suggesting lads ‘borrow’ a pair of their sisters’ tights to wear under their trousers for Ten Tors training (this does work by the way, and causes a fair amount of tent hilarity). These days thermals are readily available in synthetic, merino wool, and even bamboo fabrics. Each of these has its own pros and cons, so much so that many of the latest base layers come in blended fabrics and combine the best of one with the best of another.

We Blondes have relied on our thermals to keep us warm during long walks on the hills, through below-zero nights in tents, and after chilly wild swims. We believe we know what we are talking about on this topic after all those years of research. Here are our hard-won advantages and disadvantages of different types of thermal base layer (for both inside and outside use).

Which base layer fabric is best?

Synthetic base layers

Although synthetic materials don’t have a very good reputation when it comes to eco-credentials, they can serve a purpose when it comes to keeping you warm on chilly hill walks. Lighter weight than many of their natural fibre equivalents, synthetic thermals wash easily, dry quickly, and wear really well.

Warmth rating – good

Pack size and weight – excellent

Longevity – excellent (my Helly Hanson thermals have done years of hard labour)

Wicking properties – satisfactory

Smelliness factor – poor (synthetic thermals hold body odour and are less practical for multi-day adventures)

Environmental impact – poor (fossil fuel consumption and lack of biodegradability)

Price – excellent (especially if you are on a budget, new to your hobby or just want thermals for indoor wear)

Review – B2 discusses her super-long-lasting synthetic base layer tops.

‘I’ve had my sets of Helly Hansen polypropylene base layer tops and bottoms for as long as I can remember. They last really well, are comfortable and can be thrown in the washing machine over and over again without any ill-effect. Which is just as well because the phrase, ‘Smelly Helly’ didn’t come from nowhere. Mine are mighty convenient but I don’t like wearing them for more than one day’s hiking in a row. The tops can be worn as a single layer but the bottoms would just look baggy and weird on their own.’

If you’re looking for cheap, cheerful, and very washable (a great place to start), Blacks have a similar polyester base layer top and bottom set for just £21.

Merino wool base layers

We Blondes have said this before, and we’ll say it again. 39 million New Zealand sheep can’t be wrong. They know that the special properties of their merino wool coats repel water, and insulate from both the heat and the cold. We’ve come a long way since the days when you had to remortgage the house (or in my case visit family in New Zealand) to own a merino thermal. Most online outdoor retailers now stock them, and merino is available in blended fibres as well as on its own.

Warmth rating – excellent (my merino vests even retain heat for about 30 minutes after I take them off)

Pack size and weight – good (but often bulkier than either synthetic or bamboo base layers)

Longevity – poor (merinos are prone to both moths and ladders but are easy to mend if you don’t mind darning)

Wicking properties – excellent (merino wool will wick any amount of sweat away, for as long as you want it to)

Smelliness factor – miraculous (it never ceases to amaze me how sweet-smelling a set of three-day smelly merinos can be)

Environmental impact – sometimes controversial (animal fibres use lots of land and water, it’s also really important to look for manufacturers who stick to high animal welfare standards)

Price – good (merino thermals come in a wide range of prices but with this fibre, you really do get what you pay for)

Review – B1 tried out the Merino Union Travel Leggings (blended merino wool and polyester fibres) from Rohan. Here’s what she said…

‘I’m a firm fan of Merino leggings and these didn’t disappoint. They are as comfy as I would expect from Rohan and as warm as I would expect from our four-legged friends! The thing that I like most about these leggings compared to my old Merino ones is that they are nice and long! Tucking in a base layer top and keeping it tucked in when wriggling around a sleeping bag has proved tricky in the past. The waistband on these comes up high enough so that things stay tucked in and I have avoided the cold back patch. Perfect!’

If warmth is your priority, we can recommend Rohan’s top-quality merino blends in tops and trousers. Combining all the stretchy usefulness of synthetic with the cosiness of merino, you’re bound to be onto a winner. Plus these look great under a skirt!

Bamboo base layers

Bamboo is an interesting fabric and one you might not yet have tried. We Blondes have been impressed before with the comfort levels of bamboo tops but haven’t, until now, tried them out as an option for base layer insulation. Lovely and warm, with a good amount of stretch, bamboo fabric has plenty to recommend it.

Warmth rating – medium (what we loved about bamboo was the way it hugged the skin)

Pack size and rate – good

Longevity – inconclusive (we haven’t had much time with these yet but I hand wash all my thermals to give them a better chance at life).

Wicking properties – good (but not as quick at the job as synthetic)

Smelliness factor – good (again not as good as merino but way better than synthetic)

Environmental impact – mixed (bamboo is a great carbon-holding natural material even post-harvest but bamboo fibres require synthetic processes to gain their softness and stretchiness)

Price – mid-range (think out of the box here, e.g. yoga leggings make great thermals)

Review – B2 tried the Enduro Deep Waist Band Bamboo Leggings and the Long Sleeve Bamboo Baselayer top from BAM. Here’s what she thought:

‘Although the Enduro leggings aren’t officially sold as a thermal base layer, they do a really good job of keeping me warm under both walking trousers and jeans (especially my favourite jeans with holes in the knees). They’re great for jogging, quick to put on after chilly sea swims and look great (even on a larger bottom). I love the colourway I chose, a nice change from plain black. The top fits really well and doesn’t seem to hold much body odour. The warmth levels of both items sit somewhere between merino and synthetic. These are great products if you want cosy base layers that will also look great on their own (good for packing when we do get to go away again). I’m unsure as yet of the washability of bamboo so plan to wash these either by hand or on a delicate fabric cycle.’

If you want to try a new fabric, and enjoy fun colour-ways and designs, we recommend taking a look at BAM’s range of leggings and base layers.

Please note, BAM are currently experiencing stock issues on tops but they have plenty of leggings still available.

This post contains affiliate links. All our recommended products have been field (and home) tested by ourselves. We also have an affiliate relationship with BAM, Rohan and Blacks. Any products we don’t keep for ourselves find their way into our expedition stores. Great for us, great for you, and great for our youngsters!