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Underwear

(552 products)

Products (552)

Sort: Best Match

Top Rated
SmartwoolClassic Thermal Merino Crew Base Layer Top - Men's
$85.93 - $115.00
1506 reviews with an average rating of 4.7 out of 5 stars
tasc PerformanceElevation Merino T-Shirt - Men's
$49.73
Save 37%
compared to $79.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
38 reviews with an average rating of 4.2 out of 5 stars
REI OUTLET
Top Rated
REI Co-opMidweight Long-Sleeve Base Layer Top - Men's
$54.95
154 reviews with an average rating of 4.5 out of 5 stars
REI Co-opHeavyweight Merino Long-Sleeve Base Layer Crew Top - Men's
$49.83 - $99.95
22 reviews with an average rating of 4.4 out of 5 stars
REI Co-opMerino 185 Base Layer Top - Men's
$48.93 - $69.95
53 reviews with an average rating of 4.2 out of 5 stars
REI Co-opLightweight Half-Zip Base Layer Top - Men's
$44.95
4 reviews with an average rating of 4.8 out of 5 stars
Top Rated
SmartwoolClassic Thermal Merino Base Layer Bottoms - Men's
$115.00
615 reviews with an average rating of 4.7 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
Top Rated
SmartwoolClassic Thermal Merino Crew Base Layer Top - Men's
$85.73
Save 25%
compared to $115.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
276 reviews with an average rating of 4.7 out of 5 stars
REI OUTLET
REI Co-opHeavyweight Merino Base Layer Half-Zip Top - Men's
$49.83 - $104.95
15 reviews with an average rating of 3.9 out of 5 stars
Top Rated
SmartwoolIntraknit Thermal Merino Base Layer Quarter-Zip Top - Men's
$140.00
11 reviews with an average rating of 4.9 out of 5 stars
Top Rated
SmartwoolClassic Thermal Merino Quarter-Zip Base Layer Top - Men's
$120.00
18 reviews with an average rating of 4.6 out of 5 stars
Top Rated
Arc'teryxRho Heavyweight Base Layer Bottoms - Men's
$59.83
Save 50%
compared to $120.00
62 reviews with an average rating of 4.7 out of 5 stars
Arms of Andes160 Ultralight Alpaca Wool Crewneck Base Layer T-Shirt - Men's
$75.00
4 reviews with an average rating of 3.5 out of 5 stars
SmartwoolIntraknit Thermal Merino Pattern Crew Base Layer Top - Men's
$75.73
Save 41%
compared to $130.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
2 reviews with an average rating of 4.5 out of 5 stars
REI OUTLET
Top Rated
PatagoniaCapilene Midweight Crew Base Layer Top - Men's
$89.00
79 reviews with an average rating of 4.5 out of 5 stars
Top Rated
Arc'teryxIonia Merino Wool Base Layer Top - Men's
$90.00
38 reviews with an average rating of 4.7 out of 5 stars
SmartwoolIntraknit Active Base Layer Crew Shirt - Men's
$81.73
Save 25%
compared to $110.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
1 reviews with an average rating of 4.0 out of 5 stars
REI OUTLET
Arms of Andes160 Ultralight Alpaca Wool Long-Sleeve Base Layer Shirt - Men's
$85.00
10 reviews with an average rating of 3.6 out of 5 stars
Ortovox185 Merino Rock'n'wool Long-Sleeve Base Layer Top - Men's
$110.00
10 reviews with an average rating of 4.2 out of 5 stars
REI Co-opHeavyweight Merino Base Layer Bottoms - Men's
$29.83 - $49.83
Save 50% - 70%
compared to $99.95
7 reviews with an average rating of 4.4 out of 5 stars
Top Rated
IcebreakerMerino 200 Oasis Long-Sleeve Crewe Thermal Top - Men's
$78.73
Save 25%
compared to $105.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
64 reviews with an average rating of 4.5 out of 5 stars
REI OUTLET
Top Rated
REI Co-opMidweight Crew Base Layer Top - Toddlers'
$24.95
14 reviews with an average rating of 4.7 out of 5 stars
Top Rated
Icebreaker200 Oasis Long-Sleeve Half-Zip Base Layer Top - Men's
$115.00
17 reviews with an average rating of 4.8 out of 5 stars
Top Rated
Icebreaker200 Oasis Crewe Base Layer Top - Men's
$95.00
30 reviews with an average rating of 4.5 out of 5 stars
Top Rated
IcebreakerMerino 200 Sonebula Long-Sleeve Crewe Base Layer Top - Men's
$89.73
Save 25%
compared to $120.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
6 reviews with an average rating of 4.5 out of 5 stars
REI OUTLET
Top Rated
Arc'teryxRho Merino Wool Crew Neck Base Layer Top - Men's
$59.83 - $120.00
27 reviews with an average rating of 4.8 out of 5 stars
IcebreakerMerino 200 Sonebula Long-Sleeve High-Neck Base Layer Top - Men's
$93.73
Save 25%
compared to $125.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
2 reviews with an average rating of 5.0 out of 5 stars
REI OUTLET
Top Rated
IcebreakerMerino 260 Tech Long-Sleeve Half-Zip Base Layer Top - Men's
$135.00
34 reviews with an average rating of 4.5 out of 5 stars
ArtilectFlatiron 185 Crew Base Layer Top - Men's
$96.73 - $109.73
Save 30% - 31%
compared to $140.00 - $160.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
0 reviews
REI OUTLET

211–240 of 552 products

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

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