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  • Made of soft, non-irritating merino wool, these long underwear bottoms insulate, wick away moisture and resist odors—naturally
  • Midweight NTS 250 fabric is ideal as a single layer in cold weather and a base layer for very cold weather
  • With a UPF 50+ rating, fabric provides excellent protection against harmful ultraviolet rays
  • Flatlock seams ensure chafe-free comfort
  • Covered elastic waistband and functional fly
  • Machine washable; tumble dry low


View all Smartwool Men's Long Underwear Bottoms

REI membership


Best Use Hiking
Fabric Merino wool
Sun-Protective Fabric Yes
UPF Rating 50
Moisture Wicking Yes
Underwear Weight Midweight
Inseam (in.) 29 inches
Gender Men's

Size chart

Rated 3 out of 5 by from Huge bottom! I wanted to love these, everything about them is amazing, comfy, beautiful, they seem super warm, and they're Smartwool so you know its quailty.. but that saggy butt! Come on. When your on the trail with limited things to wear, sometimes your making breakfast or having dinner in them with other campmates.. looking like you have a full diaper is not my favorite thing, and to make them fit, they would have to be over my bellybutton? I'm 5'10, 167, 30in and bought a Small. I own 8 smart wool shirts, simply because they are so perfectly formfitting and amazing.. I hoped the same for these. Id still recommend them to someone, because everything I said here is fairly superficial and really not important on the trail. But things should still fit. Maybe I need more butt, who knows.
Date published: 2017-01-07
Rated 5 out of 5 by from Great product! Super warm and comfy. Taking these on the JMT and looking forward to toasty nights.
Date published: 2015-08-13
Rated 5 out of 5 by from Best Ever ! Purchased over 6 months ago. I wear these every night (unless in the wash) Superb comfort and temperature regulation. I'm a complete Merino wool convert. Super soft and snug, they have held their shape perfectly. I thought they were an expensive luxury, they have become an essential.
Date published: 2017-02-10
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What is the weight of the SmartWool NTS250 long underwear bottoms ?

Asked by: Ausy
​These long underwear bottoms weigh 220g or 7.76 ounces.
Answered by: REIservice
Date published: 2016-12-02

I have a size 34 waist, with 34 inseam. What is the correct size?

Asked by: JoeDaddy
We suggest a size large. This will accommodate a 34 inch waist and has an inseam of 33 inches.
Answered by: REIservice
Date published: 2016-12-12
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