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When you’re looking for thermal underwear, not just any old pair of long johns will do. Whether you’re skiing, hiking, running, hunting, or even winter camping in the frigid outdoors, you need thermal underwear that won’t let you down.
You simply can’t afford to learn about the actual quality of a product outside in winter. Even if you’re just wearing your thermal underwear indoors to save on heating costs, you want to choose with confidence before committing to your purchase.
At BestReviews, we buy the products and test them ourselves, assessing each product thoroughly. We’re like your own best friend, the one who meticulously studies each product, consults experts, and ranks each competitor. We never accept free manufacturer samples, so you can be sure that we offer impartial reviews.
Take a look at the product matrix to find some of our top selections on the best thermal underwear available.
If you want to learn more about the product in depth, you can see our shopping guide below covering types of thermal underwear, features and more.
Thermal underwear may seem like something of a luxury item. Most of us learn that stay warm in the winter, you need layering. That’s usually accomplished in the bulky form of three shirts, two sweaters and a parka.
The goal of thermal underwear is to cut some of that extensive layering. Some of the main benefits of thermal underwear include:
Thermal underwear is closely and tightly knitted; this helps retain body heat.
Some thermal underwear types are made to control odors.
Many types have a wicking quality that keeps sweat off the skin.
Certain brands are made of special materials, like synthetic or wool fabrics, that will insulate and add a level of breathability to the garment.
How well the thermal underwear handles moisture is critical. Sweating is a common downfall of traditional layering – pooling sweat draws heat away from the body through evaporative cooling. When evaporative cooling occurs, your body temperature drops as sweat evaporates. It’s the last thing you want on a cold day.
Choose thermal underwear with a looser fit when wearing it in warmer conditions.
A good set of thermal underwear is made to last. Certain brands reportedly last over 100 washes and can last up to a decade or more with good care. Follow the manufacturer’s advice on how to wash your thermal underwear, but consider some tricks to get the most life from it:
Always wash with garments of similar colors. This prevents color bleed.
Many brands allow machine washing. Follow the manufacturer's instructions, but a general rule is that hot water will lead to shrinkage.
Hand washing will not take care of odors sufficiently in most cases.
Wash thermal underwear in cold to lukewarm water. Hot water washing causes most thermal underwear to shrink.
Line dry to prevent shrinkage.
Bleach, fabric softeners, or specialty cleaners are off limits for most types of thermal underwear. Bleach will weaken those tightly woven fibers, and fabric softeners will interfere with a fabric’s wicking ability. Use a regular, mild detergent.
Merino wool may take less washing, since it controls odors so well.
Prevent wear and tear by washing with zippers zipped up.
Drying your thermal underwear on a clothes line will help prevent shrinkage.
Most thermal underwear is made from one of four main fabrics:
These are specifically made with cold weather in mind. They are usually blends of fabrics like polyester, spandex, nylon, and other synthetics materials. Most balance moisture wicking and heat retention.
Polypropylene is also a favorite synthetic fabric on the market, as it’s durable, keeps heat while wet, and wicks moisture. It also dries fast and is less expensive.
Wicking capability is a key feature of thermal underwear, as sweat contributes to the chance of hypothermia.
If you prefer something more natural, this fabric wicks moisture and keeps in the heat all on its own. It’s the original thermal underwear, dating back to classic hunters and military uses. Sometimes it’s more irritating against the skin, however.
Merino wool is a popular type of wool. It doesn’t itch or collect odors like more traditional wool might. It also maintains heat, even while wet.
Merino Wool is excellent for maintaining body heat even when the thermal underwear is wet. It’s also very odor-resistant.
This type of thermal underwear is in the less expensive range. It’s a nice option for staying warm around the home or going to an event with low physical activity, since it tends to retain moisture as you sweat.
Cotton retains moisture and shouldn’t be used for high-activity situations.
Many silks are chemically treated to enhance the fabric’s natural wicking properties.
Silk tends to wick moisture slower than the full synthetic varieties, but you can’t beat the soft feel of silk. It’s also a very thin fabric that fits well under other layers.
Some thermal underwear looks enough like daily clothing to wear as a top layer.
When selecting the best thermal underwear for your situation, there’s more to consider than just fabric type. Finding the right fabric weight is a key to comfort.
Ultralightweight, or microweight, is best suited for mild to cool weather.
Lightweight can be used in cool to moderately cold weather.
Midweight is for moderately cold to cold weather.
Heavyweight is necessary for very cold, frigid conditions.
Underwear fit is also important. If you’re looking at warmer conditions, look for looser fitting thermal underwear. The tighter the underwear is to the skin, the more it retains heat. Looser underwear allows more air circulation, leading to a lower chance of overheating. Terms such as “athletic fit” designate a tighter garment.
Sock liners accelerate wicking and help prevent skin chafing.
If sweat is not removed from your body on a cold day, it increases the risk of hypothermia and may weaken the immune system. This is why wicking qualities are so important for thermal underwear you plan to wear while active.
Chemicals like Polygiene and Aegis Microbe Shield help thermal underwear collect less odor.
Some products have a “complete” treatment system: the fabric responds to changing body conditions, providing a warming effect or cooling effect depending on your skin’s temperature.
Wicking fabrics can also wick away your body heat when temperatures rise.
Wear a base layer of fabrics with wicking properties to reduce the chance of chafing and blisters.
Try sock liners, which accelerate wicking and provide protection against friction.
Certain brands of thermal underwear come in a wide variety of patterns and colors.
Some varieties of thermal underwear come lined in comfy fleece.
For thermal shirts you plan to wear both inside and out, aim for varieties that have zippers in the front. This makes it easy to add some instant breathability.
Consider thermal shirts that with attached hoods to keep the sun off and heat in.
Don’t use bleach or fabric softener when washing your thermal underwear.
This price range has smaller, more basic items, such as thermal leggings and shorts. There are also some thermal shirts in this range, if they’re on sale. Cotton varieties are common in this price range. The higher you go in this price range, the more you see wicking technology and antimicrobial technology to keep odors at bay, especially in leggings. Silk leggings are common at the top of the price range.
These are your thermal shirts with fun designs and patterns. They may have little features like thumbholes to cover your hands more effectively. There are many synthetic fabrics in this range. Wicking technology is also typical. Silk leggings are more common in this price range.
Wash your thermal underwear with the zippers zipped to prevent damage to the garments.
Products in this price range are often made by companies that focus on eco-initiatives and sustainability goals. You’ll find more advanced technology like Polygiene odor control treatments. Complete treatment systems, which naturally regulate body temperature in either direction, are more common at these prices. Merino wool garments also become available in this price range.
In this range, tops more frequently look like a first-layer shirt. Fabrics at this range can come in greater varieties, including top-line Merino wool.
Q: How is thermal underwear better than just regular underwear?
A: The key feature of thermal underwear is its wicking technology. It literally sucks the sweat right off your body, something that regular underwear just won’t do. Many varieties keep heat in while wet, and others have benefits like odor control treatments.
Q: How do I know which type of fabric is right for me?
A: To find the variety of thermal underwear you should get, start with your level of activity. If you’re looking for something to just keep warm around the house in winter months, basic cotton varieties will work. But if you’re very active and sweating, you need wools, silks and synthetics that can wick the moisture from your body and even control odor.
The other factor to consider is the fabric weight. A good rule of thumb is that the colder the temperature you’re in, the heavier the fabric should be.
Q: Can thermal underwear be worn in all seasons, or just the coldest?
A: One great thing about thermal underwear is the sheer variety available. You can wear the heaviest, most advanced fabrics for bitterly cold winter hiking, or find microweight leggings to keep you warm at night when the temperatures start dropping in the early fall.
Q: How do I care for and wash my thermal underwear?
A: Always follow the care and washing instructions that come with your garment. Most types of thermal underwear, however, will require machine washing with gentle, basic detergent in lukewarm to cold water. Air drying also prevents shrinkage.
At BestReviews, we purchase every product we review with our own funds. We never accept anything from product manufacturers. Our goal is to be 100% objective in our analysis, and we do not want to run the risk of being swayed by products provided at no cost.