For the most part, 185 to 250 is our sweet spot for most winter sports and cold-weather activities. If you’re looking for thermal underwear that can handle many temperatures, shoot for that range, and trend lower if you run hot, or higher if you run cold. If you ski all season long, from the coldest days in January to the sunny days of April, you may want to have two (or more) sets of thermal underwear: A warmer set for cold conditions, and a lighter, more breathable set for warmer weather.

Of course, there are some downsides. Synthetic fibers often don’t have the anti-odor properties that naturally occur in certain natural fabrics, meaning they can get stinkier as you sweat. They’re also, at least in our experience, usually not as warm as high-quality natural fabric base layers. Finally, while certain recycled synthetics are responsibly sourced, some synthetics are petroleum-based, energy intensive and less sustainable than we’d like. Of course, while warmth varies with fabric weight, don’t forget to continue factoring in fabric type: A synthetic fabric that’s 200 GSM may be warmer than a natural fabric that’s 200 GSM, or vice versa. Stripe & Stare, a female-fronted certified B-Corp, make sustainable underwear designed for women who are too fun for frumpy underpants and too busy to wear anything uncomfortable.Additional Features: Some thermals come with extra features like UV protection, anti-bacterial treatments or reinforced panels in high-wear areas. The terms "thermal underwear" and "base layers" are often used interchangeably, but they can have slightly different connotations and purposes, depending on the context. While both thermal underwear and base layers are worn close to the skin to provide warmth in cold conditions, thermal underwear is typically more focused on insulation and is suited for low-activity situations. Base layers, on the other hand, offer a combination of moisture management, temperature regulation and sometimes compression, making them suitable for a wider range of activities and conditions.

Boody is also a certified B-Corp. This means the brand has been independently verified as meeting high standards of social and environmental performance, transparency and accountability. This thermal top is a lightweight layer to keep you warm and cosy on particularly chilly nights. This long-sleeved layer has a slim fit, but stretch means it’s never uncomfortable. Made from a combination of acrylic, viscose and elastane, it’s brushed on the inside to give an ultra-soft feel against the skin. A slim fit means they’ll sit as comfortably under a school uniform as they will under a snowsuit for outdoor play. There are options to fit almost any age, from toddler to teenager. There are no colour options to choose from, but this isn’t a biggie when they do their job so perfectly. We recognize that different people have different needs. Whether you’re looking for thermal underwear for extreme cold, high-intensity activities, or just everyday wear, we aimed to include a variety of options to suit diverse preferences and budgets. Lastly, the world of thermal wear is also always evolving, and we stay on top of the newest materials, technologies and trends. This ensures that our recommendations are not only reliable but also current; this story was last updated in November 2023. If you’re always finding ways to achieve the perfect silhouette to flaunt your skinny jeans or bodycon dresses, you’re in for a treat. Our shapewear makes it super easy to get a flattering body shape minus the stress of shedding a few extra pounds. For firm, full coverage, grab a shapewear bodysuit to define your curves and accentuate your natural body shape.Silk is a natural fibre that’s naturally breathable, too, which means you can also wear these leggings in the summer months to keep you cool. Thermals made of silk are basically the only thermal option that can be worn year round. Over the years, the team at Forbes Vetted has published a variety of outdoor and fitness apparel articles that feature thoroughly researched products from brands we trust. As with any industry, athletic-wear brands make many claims, and it’s our job to cut through the noise by providing solid recommendations our readers can trust. Odor Resistance: Some fabrics, particularly merino wool, have natural odor-resistant properties. For synthetic materials, look for treatments that inhibit the growth of bacteria that cause odor.

While the best underwear has all of those functional aspects, the pairs worth buying aren’t necessarily a sea of neutral-toned briefs and thongs. “Buying intimates doesn’t have to be boring,” Mara Sirhal, chief merchant and brand officer at Saks Off 5th told Bazaar. “When I shop for underwear, I look for something that represents my sense of style and makes me feel feminine and beautiful, all while being comfortable.”As well as everyday clothing, our thermals collection features thermal underwear, cosy pyjamas and thermal slippers for when the sun goes down. Thermolactyl traps the heat while elasticated waists and fur lining deliver ultimate comfort on chilly evenings. Thermals for men As well as using surplus fabrics as the main material for its products, Anekdot is committed to making the absolute most of these materials. Ethical clothing brand Rapanui makes its clothing and underwear in the UK (on the Isle of Wight), using natural materials, in its factory which is powered by renewable energy.