Thermal underwear is a must-have for winter months—the easy-to-layer garment is lightweight, tight-fitting, and thin, so it fits nicely under bulkier layers like a sweatshirt or sweatpants. Thermal underwear is particularly useful if your child plays sports or likes to hike, ski, or play in the snow. “It’s important to dress children in layers when performing those activities so that it allows them to have the optimal comfort level,” says Nilong Vyas, M.D., a board-certified pediatrician in New Orleans. That way, they can easily remove a layer once they’ve acclimated to the temperature outside. “It can take some time to acclimate to outdoor temperatures,” adds Betty Choi, M.D., a board-certified pediatrician in California. “It will take some time for the body to warm up. Initially, kids might be shivering, but once their bodies warm up with exercise, they may need to peel off extra layers so they don’t overheat,” she said. When shopping for thermal underwear, it’s important to look at the material, how thick it is, and what size you select. The best thermal underwear should be tight-fitting, breathable, and thin enough to wear underneath other clothes. Here are the best thermal underwear sets to keep kids warm this winter. This set of thermal underwear is one of our most affordable selections, so you can have extra pairs on hand when necessary. The multiple color options are helpful when matching a sports uniform, so your child can stay warm while playing their favorite organized sport. The fleece lining locks-in heat, and the moisture-wicking material keeps sweat off the skin for maximum comfort. They’re easy to wash in the washing machine and can be dried in a standard dryer. Price at time of publication: $30+ This set of stretchy tops and bottoms makes a great base layer for active kids looking to stay warm during winter sports, hikes, or skiing. Each pair is machine washable, and the two-piece set is one of the most affordable on our list. The layers are thin enough to comfortably wear underneath other clothes, but the polyester construction retains heat for protection against the cold. Although this set is only available in girls’ fit at the moment, boys may also be able to wear this base layer, as thermal underwear is supposed to fit snuggly on boys, as well. Price at time of publication: $27 This comfortable set can be layered under other clothes or worn on its own as comfy PJs. The neutral color options are suitable for boys and girls, and they look subtle when layered under brighter colors. Another big plus is that this BabyGap pick comes in a two-pack, so the per-unit price is comparable to other options on the list. Price at time of publication: $55 The polyester material helps keep heat in and moisture out. The elastic waistband and stay-put cuffs help keep the layers from riding up or down, so they’re extra comfortable for your child even when they’re on the move. This set comes in pink and blue colors and is machine washable for easy cleaning. Price at time of publication: $35 Base layers for babies should be tight and breathable, so we love this set that can be worn on its own or as a layer for a warmer outfit. The set is tight-fitting, so there’s no concern about it riding up or twisting. The snap closure at the neck makes it easy to get off, and the snap crotch is very convenient for diaper changes. The foldover mittens are an easy way to keep the baby’s little fingers warm, and the elastic waist stays in place even with little crawlers on the move. Price at time of publication: $55 This set of thermal underwear would be perfect for someone looking for a little extra warmth at bedtime or while lounging around the house. Cotton isn’t as great at wicking away moisture as some other materials, so this set wouldn’t be as ideal for activities like skiing or high-intensity sports that might involve more moisture. Price at time of publication: $75 Keep in mind that the tops and bottoms are sold separately, so this is a pricier item and should be cared for properly. The shirt comes in nine fun colors like “Festive Fuchsia Heather” and “Blueberry Hill Heather,” and the slim fit can be worn as a base layer or a top all on its own. Price at time of publication: $60 Available in four fun prints and five sizes, this durable base layer is intended for active kids who need to keep warm in colder temperatures. The patented design works to wick away sweat and moisture, keeping it off your skin and providing warmth and comfort. This set is thin and tight, so it’s easy to layer under larger pieces of clothing like ski pants or sweats. The thumbholes keep sleeves securely in place and don’t bunch up when changing into or out of additional layers. Price at time of publication: $60 These long johns are designed for medium activity levels and cold temperatures. That means they’re not an ideal choice for high-intensity sports, and they’re not suitable for super cold temperatures. Although they’re not the best bet for skiing or snowboarding, they are a great option for winter walks, hikes, or outdoor playdates. Price at time of publication: $12+ Available in five colors, this lightweight set is perfect for layering underneath larger clothes. The pants have a tight fit with an elastic waistband and cuffed ankles that stay in place even underneath bulkier layers. The top is loose-fitting, so it can be worn on its own or underneath a sweatshirt or jacket. Although this particular set is made for big kids, The North Face also has a similar toddler’s waffle base layer set available in sizes 2T through 7T. Price at time of publication: $55 Price at time of publication: $24 “Dressing in layers is always wise because the temperature can fluctuate widely from day to night and indoors to outdoors,” says Dr. Choi. “Merino wool is a natural, soft, and breathable fabric,” she adds. Merino wool is naturally insulating and comfy, so it will keep your kiddo warm even in colder temperatures. It also wicks away moisture, so it’s a great option to wear if your child will be sweating or playing in snow or rain. We love this Classic Thermal Merino Base Layer Crew by Smartwool because it’s both comfortable and stylish. Cotton is another soft, durable, and warm fabric that has a bit of stretch for added comfort. “Cotton is the best thermal underwear,” says Dr. Vyas. Our recommendation for toddlers, the BabyGap Organic Cotton Henley Set, is made with 100% organic cotton. There are a few different options to choose from, but whichever material you choose, make sure it’s breathable enough to prevent overheating. “Layers hold in warmth, so excess layers can lead to overheating. Signs of overheating include warm, flushed red skin and sweating,” Dr. Choi says. Selecting the right type of material for your child’s thermal underwear is the best way to keep them warm while avoiding overheating.
Fit
Base layers should always be tight-fitting, especially when dressing infants. “It’s important to remember that clothing for infants should always be fitted and never loose,” says Dr. Choi. Tight-fitting base layers are safer and more comfortable because they don’t bunch up or move around while out and about or during sleep. For active children playing sports or other outdoor activities, another great way to make sure that their thermal underwear stays in place is to look out for elastic waistbands or wrist and ankle cuffs, like L.L.Bean’s Wicked Warm Midweight Underwear Set. Layering can get uncomfortable, and it’s easy for arms and legs to twist and bunch up while in action. Waistband, wristcuffs, and ankle cuffs that stay securely in place can be hugely beneficial in making active kids feel more comfortable.
Care and Cleaning
As with any piece of clothing, it’s important to care for thermal underwear properly to best extend its lifespan. For the easiest experience, look for thermal underwear that’s machine washable and safe to use in the dryer. Active kids can get sweaty, and playing outside in cold temperatures often means snow, ice, and mud. To combat it all, you’ll want to find a pair that’s easy to clean and dry quickly. While most materials are machine washable, some synthetic, dry-fit materials should not be put in the dryer. Make sure to assess the care and cleaning instructions of your thermal underwear before purchasing.
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Laura Denby is a freelance product reviewer and food, home, family, and lifestyle writer. She has been testing and reviewing products for the past five years and creates thoroughly tested, comprehensive product reviews for sites like Food & Wine, Verywell Family, Real Simple, and Forbes Vetted. She is also the mother of an active one-year-old girl. “Babies don’t adjust to temperature changes as well as adults, and they also cannot tolerate heat as well as adults,” says Dr. Choi. “In addition to making less sweat, they also lose more fluid through their relatively higher skin surface area. That’s why they can get dehydrated and overheat much more quickly. Overheating can put the baby at risk for dehydration and SIDS,” she adds. Dr. Betty Choi is a pediatrician, medical writer, and mother of two. She is the author of “Human Body Learning Lab,” an interactive learning tool that gives kids a hands-on look at how the body works. She completed her medical training at Harvard Medical School and has served as an assistant clinical professor at UCLA Medical Center. Dr. Nilong Vyas is a pediatrician and Board Certified Sleep Expert. She serves as a medical review panelist for SleepFoundation.org, where she seeks to ensure that content upholds the highest standards of medical integrity. A pediatrician with Sleepless in NOLA, Dr. Vyas has been helping babies sleep safely and soundly for over eight years.
