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Underwear

(634 products)

Products (634)

Sort: Best Match

Top Rated
REI Co-opHeavyweight Merino Base Layer Bottoms - Women's
$99.95
21 reviews with an average rating of 4.5 out of 5 stars
Underwear Weight:
Heavyweight
Size Type:
Regular, Plus
REI Co-opMerino 185 Base Layer Top - Men's
$69.95
54 reviews with an average rating of 4.2 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Big
Top Rated
REI Co-opLightweight Half-Zip Base Layer Top - Men's
$44.95
7 reviews with an average rating of 4.9 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Big, Tall
tasc PerformanceElevation Merino T-Shirt - Women's
$54.73
Save 30%
compared to $79.00
78 reviews with an average rating of 4.4 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Plus
REI OUTLET
Top Rated
REI Co-opMidweight Crew Base Layer Top - Toddlers'
$24.95
15 reviews with an average rating of 4.7 out of 5 stars
Underwear Weight:
Midweight
Size Type:
Regular
REI Co-opMerino 185 Base Layer Bottoms - Men's
$79.95
129 reviews with an average rating of 4.3 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Big
Top Rated
REI Co-opMidweight Base Layer Bottoms - Toddlers'
$24.95
8 reviews with an average rating of 4.9 out of 5 stars
Underwear Weight:
Midweight
Size Type:
Regular
Top Rated
SmartwoolClassic Thermal Merino Quarter-Zip Base Layer Top - Men's
$120.00
20 reviews with an average rating of 4.7 out of 5 stars
Underwear Weight:
Midweight
Size Type:
Regular, Big
REI Co-opEveryday Boxer Briefs - Men's
$22.95
150 reviews with an average rating of 4.2 out of 5 stars
Size Type:
Regular, Big
Top Rated
REI Co-opLightweight Crew Base Layer Top - Women's
$29.95
14 reviews with an average rating of 4.8 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Plus
Top Rated
Arc'teryxRho LT Crew Neck Base Layer Top - Men's
$100.00
30 reviews with an average rating of 4.8 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Big
Top Rated
PatagoniaCapilene Midweight Zip-Neck Base Layer Top - Men's
$49.83 - $99.00
61 reviews with an average rating of 4.6 out of 5 stars
Underwear Weight:
Midweight
Size Type:
Regular, Big
SmartwoolClassic Thermal Merino Base Layer Bottoms - Women's
$81.73
Save 28%
compared to $115.00
247 reviews with an average rating of 4.4 out of 5 stars
Underwear Weight:
Midweight
Size Type:
Regular
REI OUTLET
SmartwoolClassic All-Season Merino Base Layer Bottoms - Men's
$90.00
19 reviews with an average rating of 4.2 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Big
REI Co-opMerino 185 Base Layer Bottoms - Women's
$79.95
105 reviews with an average rating of 4.3 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular
Top Rated
REI Co-opLightweight Base Layer Bottoms - Kids'
$29.95
10 reviews with an average rating of 4.7 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular
Top Rated
REI Co-opMerino 185 Long-Sleeve Half-Zip Base Layer Top - Men's
$89.95
110 reviews with an average rating of 4.6 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Big
Top Rated
REI Co-opLightweight Base Layer Crew Top - Kids'
$29.95
13 reviews with an average rating of 4.8 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular
Top Rated
Arc'teryxRho LT Zip-Neck Base Layer Top - Men's
$120.00
92 reviews with an average rating of 4.6 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Big
REI Co-opMerino Hipster Underwear - Women's
$29.95
47 reviews with an average rating of 4.0 out of 5 stars
Size Type:
Regular, Plus
Top Rated
SmartwoolClassic Thermal Merino Base Layer Bottoms - Kids'
$46.73
Save 28%
compared to $65.00
52 reviews with an average rating of 4.7 out of 5 stars
Underwear Weight:
Midweight
Size Type:
Regular
REI OUTLET
Terramar2.0 Cloud Nine Half-Zip Base Layer Top - Women's
$34.73
Save 30%
compared to $50.00
0 reviews
Underwear Weight:
Midweight
Size Type:
Regular
REI OUTLET
Kari TraaFryd Base Layer Pants - Women's
$29.83 - $65.00
15 reviews with an average rating of 3.5 out of 5 stars
Underwear Weight:
Midweight
Size Type:
Regular
REI Co-opLightweight Crew Base Layer Top - Men's
$29.95
19 reviews with an average rating of 4.5 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Big, Tall
Top Rated
REI Co-opHeavyweight Merino Long-Sleeve Base Layer Crew Top - Women's
$99.95
27 reviews with an average rating of 4.6 out of 5 stars
Underwear Weight:
Heavyweight
Size Type:
Regular, Plus
REI Co-opMerino Bikini Underwear - Women's
$27.95
49 reviews with an average rating of 4.2 out of 5 stars
Size Type:
Regular, Plus
SmartwoolClassic All-Season Merino T-Shirt - Men's
$80.00
85 reviews with an average rating of 4.1 out of 5 stars
Underwear Weight:
Lightweight
Size Type:
Regular, Big
Top Rated
PatagoniaCapilene Midweight Base Layer Bottoms - Men's
$89.00
58 reviews with an average rating of 4.5 out of 5 stars
Underwear Weight:
Midweight
Size Type:
Regular, Big
REI Co-opMerino Boxer Briefs - Men's
$39.95
104 reviews with an average rating of 4.3 out of 5 stars
Size Type:
Regular, Big
Top Rated
IcebreakerMerino 200 Oasis Long-Sleeve Crewe Thermal Top - Men's
$105.00
146 reviews with an average rating of 4.7 out of 5 stars
Underwear Weight:
Midweight
Size Type:
Regular, Big

31–60 of 634 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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