How to Choose Base Layers
REI Co-op Heavyweight Merino Base Layer Half-Zip Top - Men's
$104.95
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Get ready for adventures in the cold with our warmest merino wool base layer yet. Made with 100% merino wool, the men's REI Co-op Heavyweight Merino Half-Zip top is supersoft on the skin.
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- Heavyweight 250 g merino wool offers a soft feel without the scratchiness
- Made with 100% merino wool that naturally wicks away sweat, resists odors and dries quickly
- UPF 50+ sun protection
- Collar with half-zip neck lets you ventilate as needed
- Thumbhole cuffs hold sleeves in place and help seal warmth in
- Underarm gussets are made for ease of movement
- Shoulder seams are rolled forward to help prevent chafing under pack straps
- Close-to-body fit for optimum performance
- Back length: 28.5 in.; Tall sizes: 30.5 in.
- Weight for size M: 10.9 oz. (310 g)
- Locker loop makes it easy to hang this shirt to dry or just keep it off the ground
- Machine wash cold, use wool wash product, do not twist or wring, remove promptly; do not bleach; tumble dry low
- 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 all REI Co-op Men's Base Layer Tops| Best Use | Multisport |
|---|---|
| Shirt Type | Partial-zip |
| Fabric | 100% merino wool |
| Sun-Protective Fabric | Yes |
| UPF Rating | 50+ |
| Moisture Wicking | Yes |
| Quick Drying | Yes |
| Underwear Weight | Heavyweight |
| Sleeve Length | Long Sleeve |
| Thumbholes | Yes |
| 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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Most Helpful Favorable Review
Not A Heavyweight
dso8 months ago
Marino wool is great wet or dry...my gripe with this product was the designation as "heavyweight"....at best it is a light middle weight....not a heavy weight top.. well made but not a substantially warm undergarment...
dso
6 people found this review helpful
Most Helpful Critical Review
Not A Heavyweight
dso8 months ago
Marino wool is great wet or dry...my gripe with this product was the designation as "heavyweight"....at best it is a light middle weight....not a heavy weight top.. well made but not a substantially warm undergarment...
dso
6 people found this review helpful
Customer Images
Travelster
Received free product
Portland, OR
Warm, Itch Free, and Odor Free
8 months ago
It’s getting harder to find 100% merino base layers. This is a great one. While 100% merino may not last as long or dry as quickly as blends, I like its multi-day comfort and odor resistance for backpacking trips. At a substantial 250 grams, this top is less likely to develop those tiny holes that you eventually get with thin 100% merino base layers. The merino in this top is superfine and feels like it could be 18.5 micron, but REI doesn’t list it. Fit: True to size. I’m 5’8”, 145 lbs and the medium fits loose on me (I usually wear a small base layer top). When doing multi-day backpacking trips in cool, above freezing, weather I like to wear a thinner merino crew top under a thicker 1/4 zip merino top like this one. Construction: The top is well made with the major seams flat-lock stitched. While there is a top shoulder seam, I didn’t feel it under my backpack straps. I liked the double thick fabric cuffs but, the thumbholes were uncomfortable to use while hiking. The neck collar and front zip (YKK) were comfortable either zipped up or unzipped. I like that the top is made in a Fair Trade Certified factory and that REI is Climate Neutral Certified. What I don’t know from the online description is if the wool is certified to the Responsible Wool Standard (RWS).
Age:65–74
Weight:125–150 lbs.
Height:5'8"
Yes , I recommend this product
JohnT
Received free product
Buena Vista, CO
Great Base Layer for Adapting to Conditions
9 months ago
Before testing this Merino Top I was somewhat concerned that it would be too heavy for high effort activities. I wore it around the house for an evening with the thermostat at 65º and it was pretty warm. The next morning I headed up the local hill which has 1250’ elevation change in 1.1 mile, topping out at 9550’. Starting at 32º I quickly shed my flannel shirt and wore the merino only, still concerned that it would be too hot. As my heartrate increased I unzipped the top a bit, then even more and it quickly dumped the building heat. At the summit there was a breeze at 25º so I zipped back up and it helped hold the heat in. Heading down I began to cool down, but I was able to zip back up and not need another layer. Test two was the same mountain on a colder day. Much like the previous day I shed a layer but did just fine with only the merino. Coming down the breeze got stronger, and I did need a shell to block the wind. Test three was after 5” of new snow on the same trail. Much colder and much more work breaking trail and staying safe with spikes on the boulder-strewn trail. 20º at TH, 12º at summit. I wore a fleece mid-layer and a puffy jacket, but the puffy came off quickly. The merino and fleece were completely sufficient, changing the zip opening when needed heading up. At the summit a stiff wind required the puffy, and I wore the puffy unzipped all the way back down. I was very impressed by how well I could manage the temperature, wind, and effort changes. The 1/2 zip top (as opposed to 1/4 ones), much more efficiently dumped heat. I purposely didn’t wash the top between outings to see how it handled funk compared to synthetic fabrics. I was very pleased with how just airing it overnight kept it fresh. Care is a bit of a concern. The care instructions (printed right on the fabric rather than a label, which I really like) say to wash with a wool soap. If you don’t wear a lot of wool, you end up using product and water for just the one top. Another concern is that it is highly attractive to dog hair. My initial concern with the heavyweight top being too warm was quickly put to rest. The 1/2 zip feature easily handled the heat generated by exertion and actually helped keep me from changing layers as much. This is a welcome addition to my arsenal of gear for changing weather conditions and levels of activity.
Age:65–74
Weight:125–150 lbs.
Height:5'6"
Yes , I recommend this product
Greg
Received free product
Washington, DC
Not your grandparents' wool
8 months ago
So glad that REI finally offers merino wool garments; this one is great! I've long preferred merino wool over synthetics; I like the warmth to weight ratio, the comfort, and the natural anti-stink properties. So, with REI's entry, I'm really pleased with what they've done with this half-zip top. This shirt will be great layered as it gets colder, but it's also been great to wear by itself on chilly runs. I'm looking forward to mountain snow season and this will be perfect for that. It's really soft, doesn't need to be washed too often, and fits really well, not too tight and not too loose.
Age:45–54
Weight:175–200 lbs.
Height:6'2"
Yes , I recommend this product
Steve E
Received free product
Jamestown, TN
Nice but could use softer lining inside
8 months ago
This top is a bit itchy inside. I wish it had a softer liner on the sleeves and chest area. It was comfortable though once you got used to it. I always like thumbholes on base layers so the sleeves don't slide up under your shell jackets.
Age:45–54
Weight:225–250 lbs.
Height:6'2"
Yes , I recommend this product
Mike
Received free product
South pasadena
Black base layer
8 months ago
The overall build quality seems fine, though it does run a little small, especially the arms where the thumb loops are not usable for me as it would pull in the arms and seams too much. It’s very comfortable to wear, soft, and warm. There are other brands on the market that are of a higher quality and functionality though. I would recommend it for just a generic base layer for every day activity.
Age:45–54
Weight:150–175 lbs.
Height:6'2"
Yes , I recommend this product
gsmith
Received free product
Boston, MA
Warm base layer with great coverage
8 months ago
Very warm base layer, really smooth zipper and great coverage with long sleeves, a high neck and thumb holes to keep from your sleeves riding up from your gloves. The material is super comfortable and thick and I can see this base layer keeping me warm through the whole ski season and many to come!
Age:25–34
Weight:175–200 lbs.
Height:5'8"
Yes , I recommend this product
AT_Tekak
Short sleeves mid-weight base layer
6 months ago
Unusable thumbhole due to sleeves being too short. Is a mid-weight base layer, not heavy-weight especially when compared to a true, old heavy-weight base layer it was meant to replace. If you don't truly need a heavy base layer and don't care about thumbholes, then this could be nice for you. On top of all that.... 3 holes formed on the shoulder after one wear, one wash. They were not there before I wore it new from the store. There are no other wool clothes in my closet with bug holes, and our washing machine doesn't eat our clothes. Weak material is what that is. Returning
Height:5'8"
Age:45–54
Weight:150–175 lbs.
Yes , I recommend this product
dso
Not A Heavyweight
8 months ago
Marino wool is great wet or dry...my gripe with this product was the designation as "heavyweight"....at best it is a light middle weight....not a heavy weight top.. well made but not a substantially warm undergarment...
Jh1
Heavyweight? Compared to what?
8 months ago
Material is very thin, not heavyweight as stated. Definitely not worth the price.
Paul N
Atlanta
Simply So Good
6 months ago
One of the best base layer I had! Very warm, breath out moisture well, and no odor after exercise. Do not use a dryer after washing. Shrinks a bit.
Height:5'11"
Age:65–74
Weight:175–200 lbs.
Yes , I recommend this product
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