REI Co-op Midweight Base Layer Bottoms - Men's

Color: Alloy Gray Heather
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Members get an estimated $5.50 (10%) back on this item as a part of your annual .

Members get an estimated $5.50 (10%) back on this item.
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An ideal performance layer, the men's REI Co-op Midweight base layer bottoms boast a smooth face and low-bulk seams for easy layering and a brushed back for added warmth and comfort.


  • Recycled polyester/spandex fabric has a smooth face so layers slide on easily, and is peached for a supersoft next-to-skin layer
  • Spandex adds the right amount of stretch combined with a crotch gusset to maximize your range of motion
  • Fabric wicks moisture to keep you comfortable and dry
  • 4-way stretch delivers a flexible range of motion
  • Flatseam construction and a soft elastic waistband reduce bulk and chafing
  • UPF 50+ rating protects against sun rays
  • Average garment weight: 7.2 oz.
  • Recycled materials keep waste out of landfills; bluesign®-approved materials conserve resources and protect the health of the environment, workers and wearer (you!)
  • Made in a Fair Trade Certified™ factory, which promotes safe working conditions and sustainable livelihoods


View all REI Co-op Men's Base Layer Bottoms

Technical Specs

Best Use



92% recycled polyester/8% spandex (bluesign® approved)

Sun-Protective Fabric


UPF Rating


Moisture Wicking


Quick Drying


Fly Opening


Underwear Weight


Inseam (in.)

31 inches




Contains recycled materials

Fair Trade Certified™ factory

Contains materials that meet the bluesign® criteria

From a Climate Neutral Certified brand

Size Chart

XSSMLXLXXLXXXL24 IN Waist26 IN Waist28 IN Waist30 IN Waist31 IN Waist32 IN Waist33 IN Waist34 IN Waist35 IN Waist36 IN Waist38 IN Waist40 IN Waist42 IN Waist44 IN Waist46 IN Waist48 IN Waist50 IN Waist
Chest3536 - 3839 - 4142 - 4546 - 4950 - 5354 - 57
Sleeve Length3333.53434.53535.7536.5
Waist27.528 - 3032 - 3436 - 3840 - 4244 - 4648 - 502426283031323334353638404244464850
Hip33.534.5 - 36.537.5 - 39.541 - 4344 - 46.547.5 - 50.551.5 - 54.53233.534.536.53737.538.539.540.2541434446.547.550.552.554.5

Sizing Notes

Measurements are stated in inches unless otherwise indicated.

SHORT: Some pants are available in short sizes, which generally means an inseam that is 2.5 inches shorter than regular sizes.

TALL: Some pants, shirts, jackets and parkas are available in tall sizes, which generally means an inseam that is 3 inches longer and a rise that is 1 inch longer, a shirt or jacket body that is 2 inches longer, a parka body that is 2.5 inches longer and sleeves that are 2.5 inches longer than regular sizes.

Capri or cropped pants have an intentionally shorter inseam—reference the technical specs instead of this chart.

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