How to Choose Base Layers
REI Co-op Merino 185 Base Layer Bottoms - Men's
$79.95
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Soft, breathable and naturally odor resistant, the ultrafine merino wool of the men's REI Co-op Merino 185 base layer bottoms is just as beloved while sweating on the trail as sleeping in the tent.
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- Ultrafine 185 g merino wool offers a soft feel without any itchiness
- Made with 100% merino wool that naturally breathes, wicks away sweat, dries quickly and resists odors, making it an ideal multiday trip companion
- UPF 30 sun protection
- Flat seams and merrow stitch construction eliminate chafing
- Crotch gusset allows full range of movement
- Functional fly has the same construction as our boxer briefs
- Soft elastic waistband has a low profile so it's comfortable under other layers
- Designed to hug the body for optimum performance
- Weight: 7.4 oz. (size Large)
- Machine wash warm, gentle cycle, with wool wash product; do not twist or wring; remove promptly; do not bleach; tumble dry low; dry cleaning not recommended
- Field-tested on its own and as a base layer while hiking, running, rock climbing, cycling, skiing and camping in diverse climates across the U.S.
- REI Co-op brand is certified to The Climate Label; we actively fund efforts to reduce carbon emissions across our business and support climate projects around the world
- Made in a Fair Trade Certified™ factory
Imported.
View the REI Co-op Merino 185 Product LineView all REI Co-op Men's Base Layer Bottoms| Best Use | Multisport |
|---|---|
| Fabric | Merino wool |
| Sun-Protective Fabric | Yes |
| UPF Rating | 30 |
| Moisture Wicking | Yes |
| Quick Drying | Yes |
| Fly Opening | Yes |
| Underwear Weight | Lightweight |
| Inseam (in.) | 29 inches |
| Gender | Men's |
| Sustainability | Fair Trade Certified™ factory From a Climate Label Certified brand |
REI Co-op Clothing - Men's
| XS | S | M | L | XL | XXL | XXXL | 24 IN Waist | 26 IN Waist | 28 IN Waist | 30 IN Waist | 31 IN Waist | 32 IN Waist | 33 IN Waist | 34 IN Waist | 35 IN Waist | 36 IN Waist | 38 IN Waist | 40 IN Waist | 42 IN Waist | 44 IN Waist | 46 IN Waist | 48 IN Waist | 50 IN Waist | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chest | 35 | 36 - 38 | 39 - 41 | 42 - 45 | 46 - 49 | 50 - 53 | 54 - 57 | |||||||||||||||||
| Sleeve Length | 32 | 32.5 | 33 | 33.5 | 34 | 34.75 | 35.5 | |||||||||||||||||
| Waist | 27.5 | 28 - 30 | 32 - 34 | 36 - 38 | 40 - 42 | 44 - 46 | 48 - 50 | 24 | 26 | 28 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 38 | 40 | 42 | 44 | 46 | 48 | 50 |
| Hip | 33.5 | 34.5 - 36.5 | 37.5 - 39.5 | 41 - 43 | 44 - 46.5 | 47.5 - 50.5 | 51.5 - 54.5 | 32 | 33.5 | 34.5 | 36.5 | 37 | 37.5 | 38.5 | 39.5 | 40.25 | 41 | 43 | 44 | 46.5 | 47.5 | 50.5 | 52.5 | 54.5 |
| Inseam | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 | 32 |
Sizing Notes
Measurements are stated in inches unless otherwise indicated. Size chart values represent body measurements, not garment measurements.
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.
Inseam is measured to the floor.
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From feedback to field testing, all of our gear is dialed-in by REI Co-op members. Their adventures informed every stitch and detail—making for better, longer-lasting gear.
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Most Helpful Favorable Review
Good way to stay warm without overheating.
TonyM4 years ago
Received free productI wore these bottoms on a climb up Mt. Baker. Temps were pretty mellow, so I didn’t really test the limits, but these kept me warm overnight in the sleeping bag as well as when getting ready in the morning. As warm as I was, I never overheated during the climb. I also wore these one day on a boat trip. I wore them under shorts in windy mid-50s weather, and my legs felt fine. They did surprisingly well at preventing heat loss to the wind. I would definitely recommend these over the smart wool equivalent, as I found them more comfortable and they feel much more durable after being worn and washed. My one concern is that the elastic at the ankles doesn’t stretch very far. I found them a little difficult to pull past my heels when I was putting them on, and it seems like the most likely failure point for a tear to develop if you wear these with any frequency and have larger feet.
TonyMReceived free product
Leavenworth, WA
28 people found this review helpful
Most Helpful Critical Review
Good warmth, very bad durability.
Cameron2 years ago
This base layer worked very well, for a very short period of time. The quality of the material is not durable at all. After wearing them for less than a week (underneath 2 other layers) I had already noticed a hole near the ankle. After wearing them for 3 months, maybe 2 times a week, the material between the legs had multiple holes in and around it. I have taken care of these pants very well according to the washing instructions. I am pretty disappointed that this product didn’t stand the test of time, seeing as they were otherwise very comfortable and warm. I would not recommend to anyone who wants a base layer that will last longer than a couple trips.
Cameron
PA
32 people found this review helpful
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Cameron
Pennsylvania
Good warmth, very bad durability.
2 years ago
This base layer worked very well, for a very short period of time. The quality of the material is not durable at all. After wearing them for less than a week (underneath 2 other layers) I had already noticed a hole near the ankle. After wearing them for 3 months, maybe 2 times a week, the material between the legs had multiple holes in and around it. I have taken care of these pants very well according to the washing instructions. I am pretty disappointed that this product didn’t stand the test of time, seeing as they were otherwise very comfortable and warm. I would not recommend to anyone who wants a base layer that will last longer than a couple trips.
Age:18–24
Weight:150–175 lbs.
Height:5'11"
No, I do not recommend this product
RipNHammer73
WA
Holes after 2yrs of Light Use?
6 months ago
I purchased these in 2023. It's now Jan, 2025 and holes have developed. I'm surprised because, I made sure to wash these on the delicate cycle and air dry them. As for typical usage, I used them in November to March, about 2-3 times a week. The activity I used these for is on-shore fishing with very little walking. Based on that, I expected these bottoms to last at least 5 years. But just two years with light use? Maybe I ended up with a defective set? I feel like I should've spent the extra $25-30 for a Smart Wool set. I think REI makes awesome gear, I own a lot of their things, but these are suspect.
No, I do not recommend this product
Alaskan
Anchorage, Alaska
Solid performer at a solid price.
1 year ago
Im a wool person, it's all i buy for thermal layers, but i'm also a working stiff so i look for sales and value, these CO-OP bottoms fit the bill. You could pay twice, three times as much and not get better product. The fit and feel of these are as good if not better than any other brand i've worn. They are thicker than most base layers you encounter not like those paper thin ones that cost more and a tad looser. I run warm but i wear these under a shell layer in twentys to teens (F) thats with moderate activity like x-skiing or fat tire biking and im quite comfortable. In point of fact you could wear a thinner layer under these if so desire but i have found no need. Well done REI.
Age:45–54
Weight:175–200 lbs.
Height:5'8"
Yes , I recommend this product
tirod3
Ozarks
Great product
2 years ago
Like any good pair of boots, or jeans, initial washing and some breaking in will greatly improve your wear and perception. I have polypro thermals from the 80's sold to military and they won't ever approach the softness of merino - but we didn't care, we were warm. I have some heavy cotton duck jeans which this year finally started to soften up, and most soldiers are more than experienced in soaking a new pair of leather boots to rinse out the tannin and dye, then wearing them dry. Wash merino gently and rinse at least twice to remove the treatment a factory uses in spinning the wool and weaving it into a fabric, as it will improve it's feel and your comfort.
Age:65–74
Weight:150–175 lbs.
Height:5'6"
Yes , I recommend this product
TonyM
Received free product
Leavenworth, WA
Good way to stay warm without overheating.
4 years ago
I wore these bottoms on a climb up Mt. Baker. Temps were pretty mellow, so I didn’t really test the limits, but these kept me warm overnight in the sleeping bag as well as when getting ready in the morning. As warm as I was, I never overheated during the climb. I also wore these one day on a boat trip. I wore them under shorts in windy mid-50s weather, and my legs felt fine. They did surprisingly well at preventing heat loss to the wind. I would definitely recommend these over the smart wool equivalent, as I found them more comfortable and they feel much more durable after being worn and washed. My one concern is that the elastic at the ankles doesn’t stretch very far. I found them a little difficult to pull past my heels when I was putting them on, and it seems like the most likely failure point for a tear to develop if you wear these with any frequency and have larger feet.
Age:25–34
Weight:200–225 lbs.
Height:6'1"
Yes , I recommend this product
John W 92103
Very nice, but very poor quality fabric.
1 year ago
I really loved these, Mostly. Got a pair of these on sale 9/2023 and have worn them on 2 three day trips. So, they have been washed 3 times using mild tech wash. After the third wash, I’ve found 3 small holes. They have seen very little stress but have lasted even 2 trips. Very bad quality at ANY price, but not acceptable at REI prices (even sale prices)
No, I do not recommend this product
Jonathan
Received free product
Colorado
Just what I need.
4 years ago
My thermals are one of the things that I’m hesitant to try something new, but it was time to replace mine and I haven’t regretted giving these a chance! They’re great. Comfort is one of the most important things for me, and I’m using them whether it’s sleeping in colder weather, or out for an early morning bike ride. They seem to be true to size, maybe a little long… but are otherwise on point. Regulating temperature isn’t easy, but REI has done a great job with these.
Age:25–34
Weight:175–200 lbs.
Height:5'11"
Yes , I recommend this product
chobbes
Dublin, CA
Wish the quality was better
1 year ago
I wished this was of bettery quality and build. Very nice and comfortable base layers. The quality of stiching and construction is poor. The seams near crotch and leg joints started coming apart and developed 3 holes. Have only used it for 10+ backpacking nights and its already coming apart. I always made sure to wash them in delicate cycle. Very versatile product for both hiking and backpacking, but I would NOT recommend or buy this again.
Age:35–44
Weight:150–175 lbs.
Height:5'7"
No, I do not recommend this product
WYO
Mountain West
Just right.
2 years ago
These merino wool base layer pants are the just right combination of fabric weight and thermal efficiency. So far, they holding up to almost daily wear and regular machine washing in cold water since last November. The fit is good and close to the skin, but not binding. Minimal ride-up, or slip-down during activities. These base layer pants are light enough to make it on the “essentials list” for adventuring, and life in cold climates. They are well made with quality materials. I recommend them for anyone wanting to go “natural fiber”. Well done REI!
Weight:275–300 lbs.
Height:5'11"
Yes , I recommend this product
Anonymous
Salt Lake City, UT
Excellent Choice for your Layering Base
2 years ago
I took these and another REI polyester base layer on a 9-day Kilimanjaro hike. They were comparable but I preferred these slightly. I wore one or the other every day except in the rain forest. These fit well and were very comfortable - almost unnoticed. I felt dry even when wearing several other layers on top of these. Material and quality are great.
Age:45–54
Weight:200–225 lbs.
Height:6'2"
Yes , I recommend this product
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