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Outdoor Underwear

(512 products)

Products (512)

Sort: Best Match

Boody Eco WearClassic Bikini Underwear - Women's - Package of 2
$22.73
Save 18%
compared to $27.95
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
0 reviews
REI OUTLET
SmartwoolClassic All-Season Merino T-Shirt - Men's
$59.93 - $80.00
69 reviews with an average rating of 4.2 out of 5 stars
Top Rated
SmartwoolClassic All-Season Merino Long-Sleeve Base Layer Top - Men's
$66.93 - $90.00
64 reviews with an average rating of 4.6 out of 5 stars
SaxxVibe Super Soft Boxer Briefs - Men's
$25.73
Save 24%
compared to $34.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
26 reviews with an average rating of 4.0 out of 5 stars
REI OUTLET
Boody Eco WearPadded Shaper Bra - Package of 2
$35.73
Save 18%
compared to $43.95
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
8 reviews with an average rating of 3.6 out of 5 stars
REI OUTLET
REI Co-opMidweight Base Layer Half-Zip Top - Women's
$19.83 - $59.95
135 reviews with an average rating of 4.4 out of 5 stars
SmartwoolClassic All-Season Merino Long-Sleeve Base Layer Top - Women's
$62.93 - $90.00
116 reviews with an average rating of 4.4 out of 5 stars
Top Rated
VuoriYosemite Bra
$45.93 - $58.00
21 reviews with an average rating of 4.7 out of 5 stars
SaxxKinetic Light-Compression Mesh Boxer Brief
$28.73
Save 24%
compared to $38.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
0 reviews
REI OUTLET
Arc'teryxRho LT Base Layer Bottoms - Men's
$49.83 - $100.00
46 reviews with an average rating of 4.4 out of 5 stars
Royal RobbinsReadyDry Cami - Women's
$19.73
Save 34%
compared to $30.00
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
Top Rated
REI Co-opLightweight Long-Sleeve Crew Base Layer Top - Women's
$39.95
14 reviews with an average rating of 4.8 out of 5 stars
SaxxDropTemp Cooling Mesh Boxer Briefs - Men's
$26.73
Save 29%
compared to $38.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
41 reviews with an average rating of 3.8 out of 5 stars
REI OUTLET
Top Rated
REI Co-opMerino 185 Long-Sleeve Base Layer Top - Men's
$55.93 - $79.95
172 reviews with an average rating of 4.5 out of 5 stars
StanceButter Blend Boxers - Men's
$22.73
Save 24%
compared to $30.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
1 reviews with an average rating of 5.0 out of 5 stars
REI OUTLET
REI Co-opMerino 185 Base Layer Top - Women's
$48.93 - $69.95
44 reviews with an average rating of 4.3 out of 5 stars
Top Rated
REI Co-opMidweight Base Layer Half-Zip Top - Men's
$39.93 - $59.95
138 reviews with an average rating of 4.6 out of 5 stars
Boody Eco WearG-String Thong Underwear - Women's - Package of 2
$22.73
Save 18%
compared to $27.95
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
6 reviews with an average rating of 4.2 out of 5 stars
REI OUTLET
SmartwoolClassic All-Season Merino T-Shirt - Women's
$59.93 - $80.00
85 reviews with an average rating of 4.2 out of 5 stars
REI Co-opMerino 185 Long-Sleeve Base Layer Top - Women's
$55.93 - $79.95
199 reviews with an average rating of 4.4 out of 5 stars
BrooksCrossback 2.0 Sports Bra
$65.00
466 reviews with an average rating of 4.0 out of 5 stars
Top Rated
Beyond YogaSpacedye Lift Your Spirits Bra
$45.93 - $66.00
697 reviews with an average rating of 4.7 out of 5 stars
SmartwoolClassic Thermal Merino Base Layer Bottoms - Women's
$81.73
Save 28%
compared to $115.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
247 reviews with an average rating of 4.4 out of 5 stars
REI OUTLET
Top Rated
REI Co-opLightweight Long-Sleeve Crew Base Layer Top - Men's
$39.95
7 reviews with an average rating of 4.6 out of 5 stars
Top Rated
REI Co-opMerino 185 Long-Sleeve Half-Zip Base Layer Top - Women's
$29.83 - $89.95
99 reviews with an average rating of 4.5 out of 5 stars
RONHILLThong Underwear - Women's
$16.73
Save 32%
compared to $24.95
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
0 reviews
REI OUTLET
BrooksConvertible 2.0 Sports Bra
$60.00
97 reviews with an average rating of 3.6 out of 5 stars
Top Rated
SmartwoolClassic Thermal Merino Crew Base Layer Top - Women's
$81.73
Save 28%
compared to $115.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
367 reviews with an average rating of 4.7 out of 5 stars
REI OUTLET
RONHILLShort Underwear - Women's
$23.73
Save 32%
compared to $34.95
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
1 reviews with an average rating of 3.0 out of 5 stars
REI OUTLET
Top Rated
REI Co-opLightweight Crew Base Layer Top - Women's
$29.95
5 reviews with an average rating of 5.0 out of 5 stars
REI Co-opMidweight Long-Sleeve Base Layer Top - Women's
$54.95
244 reviews with an average rating of 4.2 out of 5 stars
tasc PerformanceElevation Merino Base Layer Bottoms - Women's
$49.73
Save 37%
compared to $79.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
53 reviews with an average rating of 4.2 out of 5 stars
REI OUTLET
SmartwoolClassic All-Season Merino Quarter-Zip Base Layer Top - Men's
$70.93 - $95.00
3 reviews with an average rating of 4.7 out of 5 stars
Top Rated
SmartwoolClassic Thermal Merino Crew Base Layer Top - Women's
$59.83 - $115.00
1149 reviews with an average rating of 4.7 out of 5 stars
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
NikeSwoosh Medium Support Bra
$40.00
115 reviews with an average rating of 4.1 out of 5 stars
Top Rated
Nani SwimwearUinta Base Layer Bottoms - Women's
$29.83
Save 60%
compared to $75.00
7 reviews with an average rating of 4.9 out of 5 stars
Top Rated
REI Co-opLightweight Crew Base Layer Top - Men's
$29.95
10 reviews with an average rating of 4.6 out of 5 stars
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
VuoriAllTheFeels Bra
$58.00
3 reviews with an average rating of 5.0 out of 5 stars
REI Co-opMerino 185 Base Layer Bottoms - Men's
$23.83 - $79.95
128 reviews with an average rating of 4.3 out of 5 stars
SmartwoolClassic Thermal Merino Base Layer Bottoms - Women's
$110.00 - $115.00
736 reviews with an average rating of 4.5 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
REI Co-opMidweight Base Layer Bottoms - Kids'
$34.95
8 reviews with an average rating of 4.6 out of 5 stars
Boody Eco WearLYOLYTE Hi-Cut Bikini Underwear - Package of 2 - Women's
$25.73
Save 19%
compared to $31.90
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
4 reviews with an average rating of 2.8 out of 5 stars
REI OUTLET
RONHILLBrief Underwear - Women's
$19.73
Save 34%
compared to $29.95
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
Boody Eco WearLYOLYTE G-String Underwear - Package of 2 - Women's
$25.73
Save 19%
compared to $31.90
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
0 reviews
REI OUTLET
Panache SportBoundless Non Wired Sports Bra
$76.00
18 reviews with an average rating of 4.3 out of 5 stars
NikeIndy High-Support Bra
$50.00
35 reviews with an average rating of 3.9 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
Panache SportEndurance Wired Sports Bra
$51.93 - $79.00
10 reviews with an average rating of 4.5 out of 5 stars
NikeIndy Light Support Bra
$38.00
32 reviews with an average rating of 4.1 out of 5 stars
Top Rated
REI Co-opLightweight Base Layer Bottoms - Men's
$39.95
10 reviews with an average rating of 4.8 out of 5 stars
Nani SwimwearUinta Base Layer Top - Women's
$29.83
Save 62%
compared to $80.00
13 reviews with an average rating of 4.5 out of 5 stars
REI Co-opMidweight Base Layer Bottoms - Men's
$54.95
77 reviews with an average rating of 4.4 out of 5 stars
Arc'teryxRho Merino Wool Zip-Neck Base Layer Top - Men's
$69.83 - $98.83
Save 29% - 50%
compared to $140.00
10 reviews with an average rating of 4.2 out of 5 stars
PatagoniaShadowlite Mid Impact Bra
$49.73
Save 27%
compared to $69.00
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-opLightweight Base Layer Tights - Women's
$39.95
7 reviews with an average rating of 4.6 out of 5 stars
REI Co-opLightweight Half-Zip Base Layer Top - Women's
$44.95
1 reviews with an average rating of 5.0 out of 5 stars
Top Rated
REI Co-opMerino 185 Long-Sleeve Half-Zip Base Layer Top - Men's
$62.93 - $89.95
102 reviews with an average rating of 4.6 out of 5 stars
CraftActive Intensity Base Layer Pants - Women's
$31.73
Save 42%
compared to $54.95
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
13 reviews with an average rating of 2.9 out of 5 stars
REI OUTLET
Top Rated
REI Co-opActive Thong Underwear - Women's
$14.95
18 reviews with an average rating of 4.6 out of 5 stars
Royal RobbinsReadyDry Full Briefs - Women's
$14.73
Save 33%
compared to $22.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
0 reviews
REI OUTLET
Top Rated
SmartwoolClassic Thermal Merino Quarter-Zip Base Layer Top - Women's
$59.83 - $120.00
28 reviews with an average rating of 4.8 out of 5 stars
CraftActive Intensity Base Layer - Women's
$36.73
Save 43%
compared to $64.95
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
3 reviews with an average rating of 3.3 out of 5 stars
REI OUTLET
tasc PerformanceElevation Merino T-Shirt - Women's
$49.73
Save 37%
compared to $79.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
76 reviews with an average rating of 4.5 out of 5 stars
REI OUTLET
BrooksPlunge 3.0 Sports Bra
$45.00
41 reviews with an average rating of 3.9 out of 5 stars
rabbitUtiliBRA-vo Sports Bra
$50.00
19 reviews with an average rating of 4.4 out of 5 stars
OiselleHi Twenty Bra
$58.00 - $68.00
1 reviews with an average rating of 5.0 out of 5 stars
tasc PerformanceElevation Merino Base Layer Bottoms - Men's
$49.73
Save 37%
compared to $79.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
31 reviews with an average rating of 3.8 out of 5 stars
REI OUTLET
SmartwoolIntraknit Active Base Layer Bottoms - Women's
$79.93
Save 27%
compared to $110.00
6 reviews with an average rating of 4.3 out of 5 stars
REI Co-opMidweight Base Layer Tights - Women's
$54.95
91 reviews with an average rating of 4.1 out of 5 stars
Helly HansenVerglas Half-Zip Top - Women's
$63.73
Save 25%
compared to $85.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
1 reviews with an average rating of 5.0 out of 5 stars
REI OUTLET
Top Rated
Beyond YogaSpacedye Slim Racerback Bra
$62.00
184 reviews with an average rating of 4.5 out of 5 stars
REI Co-opMerino 185 Base Layer Top - Women's Plus Sizes
$48.93 - $69.95
21 reviews with an average rating of 4.0 out of 5 stars
REI Co-opMerino 185 Base Layer Bottoms - Women's
$79.95
104 reviews with an average rating of 4.3 out of 5 stars
Outdoor ResearchVantage Crop Top
$38.73
Save 29%
compared to $55.00
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
Arc'teryxRho LT Zip-Neck Base Layer Top - Men's
$59.83 - $120.00
90 reviews with an average rating of 4.6 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
OnPerformance Flex Bra
$75.00
4 reviews with an average rating of 5.0 out of 5 stars
Boody Eco WearLYOLYTE Racerback Bra - Package of 2
$43.73
Save 18%
compared to $53.90
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
Terramar1.0 All-Season Lightweight Merino Wool T-Shirt - Women's
$34.73
Save 30%
compared to $50.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
0 reviews
REI OUTLET
Top Rated
REI Co-opHeavyweight Merino Base Layer Bottoms - Women's
$29.83 - $69.93
Save 30% - 70%
compared to $99.95
18 reviews with an average rating of 4.6 out of 5 stars
Top Rated
REI Co-opHeavyweight Merino Long-Sleeve Base Layer Crew Top - Women's
$29.83 - $99.95
25 reviews with an average rating of 4.6 out of 5 stars
Top Rated
Arc'teryxRho LT Crew Neck Base Layer Top - Men's
$59.83 - $100.00
27 reviews with an average rating of 4.8 out of 5 stars
SmartwoolClassic All-Season Merino Base Layer Bottoms - Women's
$90.00
16 reviews with an average rating of 4.4 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
SmartwoolIntraknit Racerback Bra
$48.73
Save 25%
compared to $65.00
Members use code OUT4JUL25 for $20 off $100+ at REI Outlet
8 reviews with an average rating of 3.5 out of 5 stars
REI OUTLET
Top Rated
RHONERevive Longline Bra
$45.93 - $58.00
67 reviews with an average rating of 4.9 out of 5 stars
PatagoniaCapilene Thermal Weight Long Underwear Bottoms - Women's
$99.00
14 reviews with an average rating of 3.6 out of 5 stars

1–90 of 512 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