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  • Merino wool helps maintain comfort whether the climate is warm, cold or in-between
  • With a UPF 50+ rating, fabric provides excellent protection against harmful ultraviolet rays
  • Chafe-free flatlock seams enhance comfort
  • Wide, soft waistband enhances fit
  • Functional fly, close-to-skin fit and natural rise
  • The men's Smartwool Midweight long underwear bottoms do not itch and will not shrink; machine wash and dry


View all Smartwool Men's Long Underwear Bottoms

REI membership


Best Use Multisport
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 5 out of 5 by from 2nd Set After hearing me rave about my SmartWool long underwear during the last couple of cold Ohio winters, my husband decided to try a set of his own on a fishing trip in March near the shores of Lake Erie. He's a convert now. He couldn't believe how comfortable they are, and they did a great job of keeping him warm in his waders out in the cold water and hiking through the snow. He's a tall, slim guy (6'3" and 160), and the Medium fit him perfectly, and actually came down to his ankles (usually long underwear stop at mid-calf for him). He started wearing them to work when he needed to be in unfinished, cold spaces, and so this was a purchase of a second set.
Date published: 2013-07-16
Rated 1 out of 5 by from Not what they used to be! I have purchased three sets (top/bottom) of this product over the years. The bottoms were 'updated' a bit over a year ago to have a wider waistband that is seamed in the front. First of this 'improved' type bottom was purchased in February, the waistband started to come apart in three months. In July, it completely separated. REI replaced the failed product in August. It is now December..and the waistband in THAT product is completely separated. I have an OLDER bottom that is four years old. I've worn it pretty much to tatters...but the WAISTBAND? It is still PERFECT. SmartWool has the basis of an excellent product. NO OTHER undergarment has performed as well at its job as does this merino wool product. The QUALITY however, has taken a long jump off a big cliff. I did contact SmartWool about the issue, hoping to help them help themselves. They did not bother with a response of any kind. REI on the other hand, continues to support their customers. Kudos to REI. Nothing of the sort to SmartWool.
Date published: 2014-12-17
Rated 5 out of 5 by from Outstanding! I have owned many different types of base layer before being converted to merino wool and I am not looking back. The top of the pants and leg cuffs are comfortable. The crotch area is gusseted and unrestricted. Absolutely works as advertised!
Date published: 2013-02-22
Rated 5 out of 5 by from warmth and comfort This was probably a little pricier than I wanted, but it goes to show that you get what you pay for. These long johns were warm, wicked very well, and were totally comfortable.
Date published: 2014-10-03
Rated 5 out of 5 by from Life-changing Long Johns Boy, have times changed! No more white waffle-knit cotton long johns for me - these SmartWool base layer bottoms have completely transformed my skiing experience! They are super soft, extremely comfortable, and incredibly effective at wicking away moisture and odor! I'm totally hooked and won't wear anything else under my ski pants now! I went to REI in a semi-panic because I waited too long before a major ski trip, and I grabbed these - which turned out to be the last pair of SmartWool base layer bottoms in the store. I wasn't sure whether I needed mid-weight or lightweight, but at that point, I had no choice...and for spring skiing (first week of March) in Telluride, CO, they were perfect. I wondered if I might be too warm, but I was perfectly comfortable from 9:30 a.m. - 3:30 p.m. with temps in the 20s/30s on the mountain and up to 40 at the base. Pretty amazing, really. I never once thought about whether I was too cold or too warm - which was a new experience for me, as I'd always associated skiing with various kinds of physical discomfort. And after three full days in a row, they still smelled fresh at the end of my trip! (Gross to think about it, but it's one of the nice things about merino wool, and I have to confirm that it's true!) Yes, they are very expensive. I couldn't believe what I was going to pay to get them. But after all I'd heard about them, I really wanted to test them out, and I am extremely happy with them. It's an investment, and it pays off handsomely in comfort and function. Highly recommended.
Date published: 2015-04-14
Rated 5 out of 5 by from Warm, comfortable, awesome I've had a set of midweight (top and bottom) long underwear for 2 winters, not counting this one. It's fantastically warm like no cotton can ever feel, it's amazingly soft and comfortable, and it's lasted quite a long time with daily usage in the cooler months. I recommend Smartwool underwear 100%.
Date published: 2013-01-04
Rated 5 out of 5 by from So Comfy!! These are the 260g weight underwear. The bottoms come up to just below the calf muscle, which fine, I have long legs. My long socks fill the gap anyways. Very comfortable, I wear them all the time around the house too. Its been warmer here in Colorado so I haven't been snowboarding in cold cold temps, I am sure they will do better than my last pair (Icebreaker 150g). Woman I get why you love yoga pants and leggings so comfy!!
Date published: 2016-02-28
Rated 5 out of 5 by from Awesome! Comfortable, added warmth but not too warm inside
Date published: 2013-11-23
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