Does thermal underwear really work?

Thermal underwear is a fantastic way to keep kids warm in lower temperatures. “In frigid cold weather, thermal underwear can keep a child warm and safe from frostbite,” says Dr. Choi. As long as you select a pair of lightweight or midweight thermals made from a warm, breathable material, these thin layers are a great way to lock in heat and keep out moisture.

What is the warmest type of thermal underwear?

Thermal underwear should be made from cozy material that’s breathable, and some of the warmest materials are cotton and merino wool. Merino wool is a thinner, softer version of standard wool, which provides the same amount of warmth but makes it easier and more comfortable to wear against the skin. Merino wool is naturally moisture-wicking, which means it will keep you dry, too. Our favorite merino wool piece is the Classic Thermal Merino Base Layer Crew by Smartwool .

Why does my kid's thermal underwear label say it is not intended for sleepwear?

Layering too much can cause overheating, which is dangerous in children of all ages. Some types of dry-fit thermal underwear aren't as breathable as others, which means they hold in heat and restrict airflow. Being mindful of overheating is particularly important with infants, so if your thermal underwear is labeled “Not intended for sleepwear,” it’s best to avoid it. “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.

How much should thermals cost?

Thermal underwear is a relatively inexpensive item. Depending on the type of material you select and the brand that makes it, a set of thermal underwear for kids can range between $20 and $60. Our most affordable pick is the $12 Fruit of the Loom Waffle Set , which is very comfortable and can also be used as PJs; however, the light set is not recommended for super cold weather. On the opposite end of the price range, the Burton Kids Fleece Base Layer Set and the Classic Thermal Merino Base Layer Crew by Smartwool are both $60 but offer top-notch warmth and protection.

The Best Thermal Underwear for Kids of 2023

The Best Thermal Underwear for Kids of 2022 — The North Face / Amazon

Kids don’t stop when the temperature drops, so being prepared for cold-weather play is crucial. Making sure they’re warm yet comfortable enough to move around is a balance that’s hard to strike—bundling up can impede mobility and even cause overheating. That’s why dressing your child in layers is your best bet for keeping them warm yet comfortable. And one of the best ways to get prepared for winter is to have a set of breathable, lightweight, and warm thermal underwear on hand.

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.

Our Top Picks

Best Overall:

Rocky Thermal Underwear For Boys at Amazon

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Best Budget:

Thermajane Girls Thermal Underwear Set for Kids at Amazon

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Best for Toddlers:

BabyGap Organic Cotton Henley Set at Gap.com

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Best for Toddlers Runner Up:

L.L. Bean Wicked Warm Midweight Underwear Set at L.L.Bean

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Best for Babies:

Patagonia Capilene Midweight Base Layer Set at Patagonia.com

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Best Cotton:

Gap Kids’ 100% Organic Cotton Henley Set at Gap.com

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Best Merino Wool:

Smartwool Kids’ Classic Thermal Merino Base Layer Crew at REI

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Best Ski Base Layer:

Burton Kids’ Fleece Base Layer Set at Amazon

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Best Kids’ Long Johns:

Fruit of the Loom Kids’ Waffle Thermal Underwear at Amazon

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Best for Hiking:

The North Face Big Kid’s Waffle Base Layer Set at Nordstrom

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In This Article

Our Picks
What to Look For in Thermal Underwear for Kids
FAQ
Why Trust VeryWell Family

Amazon

Pros

Fleece-lined for added warmth
Elastic waistband stays in place
Flat seams prevent chafing

Cons

Tend to run large
No thumbholes

In order for thermal underwear to be effective and comfortable, it needs to be warm, stretchy, and breathable. That’s why we love this pair from Rocky Thermal. Made from a polyester blend, the tight-fitting thermal underwear is lined with fleece, and the seams are made with elastic to provide ultimate comfort during active days. Available in 10 colors and five sizes for boys and nine colors and five sizes for girls, this is a versatile option that’s perfect for any type of cold weather activity.

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+

Material: Polyester blend | Sizes available: Youth XS, S, M, L, XL | Care instructions: Machine washable

Amazon

Pros

Tagless design makes them extra comfortable
Spandex construction adds extra stretch
Elastic waistband keeps them in place

Cons

Not available in boys’ fit

This set of budget-friendly thermal underwear is designed to keep kids warm, comfortable, and dry. Made from polyester and spandex, each set boasts a four-way stretch that allows for maximum mobility while playing, walking, or running. The elastic waistband keeps the bottoms securely in place, and the tagless design prevents scratching or itching. The ultra-soft fleece comes in a variety of styles, so this is a versatile option for all types of activities.

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

Material: Polyester and spandex | Sizes available: Youth XS, S, M, L, XL | Care instructions: Machine washable

Gap

Pros

Organic cotton is natural and soft
Also available in infant sizes
Elastic waistband keeps them in place
Comes in an two-pack

Cons

Only available up to size 5

Toddlers are an active bunch, and their soft skin can be sensitive. That’s why it’s a great idea to dress babies and toddlers in comfortable, breathable clothing made from natural fabrics. This set by BabyGap is made from 100% organic cotton, so it’s warm, breathable, and naturally non-toxic. This two-piece Henley set comes with a top and a bottom that boast elastic wristbands and waistbands, so your little crawler or walker can cruise around while their clothes stay securely in place.

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

Material: Organic cotton | Sizes available: 6-12, 12-18, and 18-24 months; 2, 3, 4, and 5 years | Care instructions: Machine washable

L.L. Bean

Pros

Available in boys and girls styles
Midweight is warm but not stuffy
Cuffs keep pants and sleeves in place

Cons

Only available in two colors
Limited sizes

One of the challenging parts of having a toddler is dressing them appropriately. If your young one isn’t verbal yet, it can be tough to know if they’re comfortable. You always want your child to be warm enough, but it’s important to be careful of overheating, too. That’s why we love this midweight option. It provides just the right amount of warmth for winter months, and it’s an easy option for layering. The top and bottom set is warm enough to be worn on its own, but it’s a great option for layering under sweaters and sweatpants in super cold weather.

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

Material: Polyester | Sizes available: 2T, 3T, 4T | Care instructions: Machine washable

Backcountry

Pros

Fold-over mittens keep little fingers warm
Knee patches add durability for crawlers
Snap-neck makes it easy to get on and off

Cons

Only available in one pattern

Keeping babies at a comfortable temperature can be challenging during those first few months. Depending on what month your baby was born and what climate you live in, you may find the need to introduce a base layer at some point during the first year. “Babies don't adjust to temperature changes as well as adults,” says Dr. Choi. “Because babies are much smaller than adults, their skin's surface area is much greater compared to their body weight. Thus, they can lose a lot of heat through unclothed skin and cannot tolerate cold as well as adults,” she says.

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

Material: Recycled polyester | Sizes available: Newborn and 3, 6, 12, 18, and 24 months | Care instructions: Machine washable

Gap

Pros

Set of two
Elastic waist keeps pants in place

Cons

Cotton doesn’t wick away moisture as well as other materials

Organic cotton is a fantastic option for thermal underwear because it’s soft, warm, and cozy. Whether your kiddo wears this thermal underwear set to sleep, play sports, or go for a hike, it's a comfortable option for any adventure—cotton offers a gentle amount of natural stretch with an unmistakably soft feel. We love that this selection comes with two sets, so you always have a backup pair, no matter what type of weather you’re facing. Cotton is also super easy to clean, so it’s a great option for active kids who like to get dirty.

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

Material: 100% cotton | Sizes available: 6, 8, 10, 12, 14 | Care instructions: Machine washable

Smartwool

Pros

Flat seams add comfort
Interlocking knit helps enhance breathability and airflow

Cons

Top and bottom sold separately
Dry cleaning preferred

Merino wool is a preferred material for layering because it’s warm, soft, breathable, and naturally moisture-wicking. This kids’ thermal shirt is a great way to keep warm during any adventure, thanks to the specific construction of the material. Made from 100% merino wool, the material is knit in an interlocking fashion that helps improve breathability, thermoregulation, and comfort. The wool naturally wicks away moisture and removes it from your skin, which also helps promote odor regulation. We love that the flat seams add coziness and prevent chafing, so this is a comfortable item to wear while playing outdoor sports, skiing, walking, or hiking.

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

Material: Merino wool | Sizes available: Youth XXS, XS, S, M, L, XL | Care instructions: Machine wash on gentle cycle, tumble dry on low, dry cleaning preferred

Amazon

Pros

Spandex adds extra stretch
Thumbholes keep sleeves in place
Elastic waistband keeps pants in place

Cons

Doesn’t have ankle cuffs

For active kids who love to ski, it’s essential to find a base layer that will keep them warm and dry and move with them as they head down the mountain. This set from Burton easily hits all of those requirements. The spandex and polyester set is designed with flat seams to prevent chafing and an anti-pilling fleece that locks in heat. Added stretch ensures comfortability with any kind of exercise so your kids can run, jump, twist, and turn without any pulling or bunching.

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

Material: Polyester and spandex | Sizes available: Youth XS, S, M, L, XL | Care instructions: Machine washable

Amazon

Pros

Spandex collar and cuffs keep clothing in place
Waffle knit adds comfort and warmth

Cons

Not designed for super-cold temperatures

Long johns are some of the coziest pieces of clothing anyone can wear. Waffle fabric adds texture and locks in heat, so this top and bottom set from Fruit of the Loom is warm, soft, and ultra-comfortable. Available in 11 colors and prints for boys and eight colors and prints for girls, this cozy set is perfect for daily winter wear. The spandex collar and stretchy knit make for a great base layer while out and about, but the lightweight, waffled material means they’re a cozy option for sleepwear, too.

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+

Material: Polyester and cotton | Sizes available: 4-5, 6-7, 7-8, 10-12, 14-16, 18 | Care instructions: Machine washable

The North Face

Pros

Waffle knit adds comfort and warmth
Cuffed collar, sleeves, and ankles stay in place
Dry fit technology keeps moisture away

Cons

Top has a looser fit

Hiking outdoors can get cold, especially if you’re traversing different altitudes or types of shaded terrain. Wearing multiple layers is essential, and it’s particularly important to find thermal underwear that wicks away moisture. This waffled set from North Face will keep you warm and dry, thanks to the patented FlashDry technology that wicks away moisture from the skin. Made from recycled polyester, this set of thermal underwear aims to lock in heat while promoting airflow at the same time.

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

Material: Recycled polyester | Sizes available: Youth XS, S, M, L, XL, XXL | Care instructions: Machine washable

Amazon

Pros

Dual-layer fabric provides extra warmth
Quick-dry fabric keeps moisture away
Four-way stretch is ideal for active kids

Cons

Doesn’t have thumbholes

Active kids need a base layer that will move with them, so we love that this set is made with spandex for optimal mobility. The compression-style set is tight-fitting, so it won’t bunch or twist underneath uniforms or sweatpants. The stretchy fabric is lined with fleece, so these can easily be worn outside during cold months—which makes them perfect for soccer, football, or cross-country sports seasons. The quick-dry fabric aims to remove sweat and moisture from the skin, keeping your child dry, warm, and comfortable throughout the day.

Price at time of publication: $24

Material: Polyester and spandex | Sizes available: Youth XS, S, M, L, XL | Care instructions: Machine wash, low tumble dry, do not iron

What to Look For in Thermal Underwear for Kids

Material

Thermal underwear should be made from lightweight, breathable material that moves easily with your active kids. Before selecting a pair, make sure to assess when and where your kids will be wearing them. If you’re looking for a set to wear underneath a uniform for outdoor sports, you’ll want to select a pair that is made with spandex for added stretch, like the TELALEO Thermal Compression Base Layer. If you want your kiddos to wear their base layer under a big bulky sweater, you’ll want something soft and cozy, like this Organic Cotton Henley Set by Gap.

“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.

Frequently Asked Questions

Does thermal underwear really work?

Thermal underwear is a fantastic way to keep kids warm in lower temperatures. “In frigid cold weather, thermal underwear can keep a child warm and safe from frostbite,” says Dr. Choi. As long as you select a pair of lightweight or midweight thermals made from a warm, breathable material, these thin layers are a great way to lock in heat and keep out moisture.
What is the warmest type of thermal underwear?

Thermal underwear should be made from cozy material that’s breathable, and some of the warmest materials are cotton and merino wool. Merino wool is a thinner, softer version of standard wool, which provides the same amount of warmth but makes it easier and more comfortable to wear against the skin. Merino wool is naturally moisture-wicking, which means it will keep you dry, too. Our favorite merino wool piece is the Classic Thermal Merino Base Layer Crew by Smartwool.
Why does my kid's thermal underwear label say it is not intended for sleepwear?

Layering too much can cause overheating, which is dangerous in children of all ages. Some types of dry-fit thermal underwear aren't as breathable as others, which means they hold in heat and restrict airflow. Being mindful of overheating is particularly important with infants, so if your thermal underwear is labeled “Not intended for sleepwear,” it’s best to avoid it.
“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.
How much should thermals cost?

Thermal underwear is a relatively inexpensive item. Depending on the type of material you select and the brand that makes it, a set of thermal underwear for kids can range between $20 and $60. Our most affordable pick is the $12 Fruit of the Loom Waffle Set, which is very comfortable and can also be used as PJs; however, the light set is not recommended for super cold weather. On the opposite end of the price range, the Burton Kids Fleece Base Layer Set and the Classic Thermal Merino Base Layer Crew by Smartwool are both $60 but offer top-notch warmth and protection.

Why Trust VeryWell Family

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.

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.