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Long thermal underwear

Even on the coldest of days, with long thermal underwear on, the winter weather is all very bearable. This is truly the secret to keeping warm - starting off with putting on long underwear to combat the cold temperatures and winds. It is an essential and a critical part of your winter wardrobe.

You might know long underwear by some other names like "thermal underwear", "long johns", "thermal wear" "thermals", "base layer" or "polypropylene underwear", "cotton or silk thermal underwear".

Why wear long thermal underwear?

It's all about keeping you warm and dry. The purpose of this fitted layer is to wick away moisture and trap your body heat next to your skin so you retain heat longer thereby keeping warm.

Wearing long thermal underwear in winter makes any outdoor activity way more comfortable, safe and warm. By layering your clothes starting with thermal underwear, followed by a middle more bulky layer and then finally, an outer waterproof layer makes your winter so much more enjoyable. Not to mention that if you are outside for long periods of time, wearing this important inner layer helps minimize winter dangers like hypothermia. Sports enthusiasts rely on this crucial layer to allow them to enjoy what they do.


There are only two styles to buy:

  • One piece thermal underwear suit or
  • Two piece bought separately as a long-sleeved top and a lower body piece covering the waist to the ankles.

Both kinds can be very close fitting and contoured to fit your body or they can be looser fitting. It all depends on the type of fabric e.g. with a cotton blend, the thermal underwear is likely to be looser fitting whereas the micro fibers are more form fitting and tend to keep their shape better than the cotton types.


You'll find that fabric thickness, knitted or smooth texture, type of weave, and brand type all create differences in the type of long thermal underwear available to you. Buying the right kind of thermal underwear depends on what you want it for. You can get light, mid-weight and heavy weight thermal underwear.

Here's my recommendation:

  • Indoors - lighter fabrics like silk, cotton, cotton/poly blend, poly/spandex
  • Outdoors - mid to heavy weight is necessary like a wool/micro-fiber blend.

Your choice will also depend on the kind of winter climate you live in as well e.g. you do have mild winters or very cold, snowy ones? Having several sets of both lightweight and heavier weight thermal underwear makes the most sense. It gives you great flexibility to adapt to any kind of winter weather.


You'll find a wide variety of natural and synthetic fabrics is used for long thermal underwear.

  • Natural fibers include fine (merino) wool, cotton, hemp, bamboo and silk
  • Synthetics include acrylics, polyester, nylon, polypropylene and spandex.

The man-made fibers sold today combine both natural and man-made materials in different combinations to produce the best of both worlds to keep you warm and dry.

A more recent entry is bamboo. It's now being used in the rush to produce more eco-friendly renewable clothing. When I think of bamboo, I think of large bamboo swaying in a tropical breeze not something that I could wear! However, bamboo fabric is very light, incredibly soft, and feels great against your skin.


  • As for cotton thermal underwear, it's not that good to wear as an inside layer, particularly if you are doing hard physical exercise outdoors. Wearing cotton inside is fine but outside, once cotton gets wet, the moisture is not wicked away. It will leave you feeling cold and wet that encourages more heat loss from your body's core. Not a good thing! Still, wearing cotton or cotton flannel is great for sitting around a crackling fire in your living room drinking hot chocolate or sipping mulled wine.


  • Silk thermal underwear feels great against your skin, as it's warm and thin leaving a little more room I think. However, I've found that silk thermal underwear does not last longer than a few seasons of wear and tear. It's also more expensive to buy or replace than man-made synthetics too.


  • Fine, thin wools or wool blends work well but if you are allergic to wool, it may irritate your skin. Also, once wool starts to absorb water, it becomes quite heavy to wear comfortably.

I like the next-to-the skin layer to be as light as possible because my other layers are going to be bulkier and thicker so I opt for poly/spandex with a dash of cotton blend for both indoor and outdoor use. They wash well and last for quite a few seasons before I have to replace them.


The most common colours for thermal underwear tend to be white, grey, light blue, beige and black.

  • Cotton/poly/spandex blends and silk types are made in many colours and some patterns but the most common ones tend to be solid colours such as white, grey, light blue and beige
  • Micro fibers/synthetics/wool tend to be darker like blue and black although you can get lighter colours with some searching.

Keeping the white thermal underwear white may need some special washing treatment on occasion. Keep in mind that the white will begin to look more like light grey overtime with repeated washings over several winter seasons.

Odor-reducing and anti-bacterial materials

Recent modern materials have other benefits manufactured into them like anti-bacterial and odor-reducing qualities now. Generally, these fabrics provide a better fit and some manufacturers also claim their products improve blood circulation! Even when you are sweating buckets from doing heavy exercise like cross-country skiing or jogging, the man-made thermal underwear quickly moves the moisture away from your skin so you don't feel so cold or damp.

Buying long thermal underwear

You can get long thermal underwear for everyone in your family including infant and toddler thermal underwear, children's thermal underwear and of course, women's and men's thermal underwear.

How to decide on the best thermal underwear to buy depends on a few different factors such as:

  • Purpose in buying - everyday use, winter sports or camping, clearing snow?
  • Comfort - it's next to your skin so what fabric is best and most comfortable for you?
  • Warmth - how warm do you want the material to be, light or more heavier weight?
  • Price - how much do you want to spend?
  • Readily available - can you easily find what you need from different local stores/online?
  • Life of use - how long do you want them to last?

Caring for your long thermal underwear

Whatever you are caring for, always remember to read the manufacturer's instructions to get the most out of your winter thermal underwear.

Micro fiber/Poly/Spandex

  • The synthetic fabrics last several seasons, are easy to care for and dry quickly. Washing them inside out is usually recommended as well. Although they are generally dryer-safe, hanging them up to dry is better.


  • It's best to wash cotton thermal long underwear in a cold water cycle to prevent them from shrinking. I've had cotton ones shrink using the warm water cycle by mistake (definitely not the hot water cycle, as it will shrink them for sure!). Drying them too can be tricky so let them dry naturally lying flat on a towel or over a towel on a rack. You can certainly hang them up to dry but they may lose their shape a little. Using a warm dryer cycle will probably shrink your long cotton underwear although just machine air-dry tends to be fine. However, to be on the really safe side, let them air-dry naturally.


  • If you have a wool or a wool blend then the same rules for cotton apply (cold water wash only!). Otherwise, they will shrink, lose some of their shape and you'll have to replace them.


  • For silk long underwear, you can hand-wash them or use the 'delicate' cycle of your washing machine. Even though silk is a very strong natural fiber, after a few seasons the weave seems to weaken and holes gradually appear.

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