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Boys Thermal Underwear

(21 products)

Products (21)

Sort: Best Match

SmartwoolClassic Thermal Merino Crew Base Layer Top - Kids'
$44.73
Save 31%
compared to $65.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
5 reviews with an average rating of 3.6 out of 5 stars
REI OUTLET
Top Rated
SmartwoolClassic Thermal Merino Base Layer Bottoms - Kids'
$48.73
Save 25%
compared to $65.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
52 reviews with an average rating of 4.7 out of 5 stars
REI OUTLET
SmartwoolClassic Thermal Merino Base Layer Quarter-Zip - Kids'
$51.73
Save 26%
compared to $70.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
0 reviews
REI OUTLET
Top Rated
IcebreakerMerino 260 Tech Thermal Base Layer Leggings - Kids'
$49.73
Save 28%
compared to $70.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
7 reviews with an average rating of 5.0 out of 5 stars
REI OUTLET
IcebreakerMerino 260 Tech Long-Sleeve Half-Zip Thermal Base Layer Top - Kids'
$52.73
Save 29%
compared to $75.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
4 reviews with an average rating of 4.5 out of 5 stars
REI OUTLET
SmartwoolClassic Thermal Merino Base Layer Hoodie - Kids'
$51.73
Save 31%
compared to $75.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
3 reviews with an average rating of 4.7 out of 5 stars
REI OUTLET
Top Rated
REI Co-opMidweight Base Layer Bottoms - Kids'
$34.95
8 reviews with an average rating of 4.6 out of 5 stars
Top Rated
REI Co-opLightweight Base Layer Bottoms - Kids'
$29.95
9 reviews with an average rating of 4.7 out of 5 stars
PatagoniaCapilene Thermal Weight Long-Underwear Bottoms - Men's
$99.00
14 reviews with an average rating of 4.0 out of 5 stars
Top Rated
REI Co-opMidweight Base Layer Crew Top - Kids'
$34.95
5 reviews with an average rating of 5.0 out of 5 stars
SmartwoolClassic Thermal Merino Base Layer Bottoms - Kids'
$44.93
Save 30%
compared to $65.00
0 reviews
PatagoniaCapilene Midweight Base Layer Bottoms - Kids'
$26.93
Save 30%
compared to $39.00
5 reviews with an average rating of 2.4 out of 5 stars
Helly HansenLifa Merino Midweight Base Layer Set - Kids'
$69.73
Save 30%
compared to $100.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
2 reviews with an average rating of 4.0 out of 5 stars
REI OUTLET
Top Rated
IcebreakerMerino 200 Oasis Long-Sleeve Base Layer Crew Top - Kids'
$41.93 - $60.00
8 reviews with an average rating of 4.5 out of 5 stars
Helly HansenMerino Wool Base Layer Set - Kids'
$75.73
Save 36%
compared to $120.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
0 reviews
REI OUTLET
Top Rated
REI Co-opMerino Midweight Base Layer Bottoms - Kids'
$49.95
15 reviews with an average rating of 4.5 out of 5 stars
Top Rated
REI Co-opMerino Midweight Base Layer Crew Top - Kids'
$49.95
25 reviews with an average rating of 4.7 out of 5 stars
IcebreakerMerino 200 Oasis Base Layer Leggings - Kids'
$41.93
Save 30%
compared to $60.00
6 reviews with an average rating of 3.8 out of 5 stars
Helly HansenLIFA Merino Midweight Base Layer Set - Kids'
$100.00
1 reviews with an average rating of 4.0 out of 5 stars
Helly HansenHH LIFA Base Layer Set - Kids'
$70.00
1 reviews with an average rating of 1.0 out of 5 stars
Helly HansenGraphic Lifa Merino Base Layer Set - Kids'
$74.73
Save 32%
compared to $110.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
1 reviews with an average rating of 1.0 out of 5 stars
REI OUTLET

Sort: Best Match

Related Expert Advice articles

What material is best?

Wool is moisture-wicking and odor-resistant, while synthetic fabrics are more durable and less expensive.

Match the temp to the trek

Lightweight layers are best for moderate to cool temperatures. Midweight layers are best for cold temperatures. Heavyweight layers are best for below-freezing temperatures.

Find your fit

To be able to wick sweat efficiently, your next-to-skin layer needs to actually be next to your skin. A comfortably snug fit everywhere is your goal.

Read full article: How to Choose Base Layers