How to Choose Base Layers

Get ready for adventures in the cold with our warmest merino wool base layer yet. Made with 100% merino wool, the women's REI Co-op Heavyweight Merino Half-Zip top is supersoft on the skin.
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Imported.
View all REI Co-op Women's Base Layer TopsBest Use | Multisport |
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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 | Women's |
Sustainability | Fair Trade Certified™ factory From a Climate Label Certified brand |
XXS | XS | S | M | L | XL | 1X | 2X | 3X | 0 | 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18W | 20W | 22W | 24W | 26W | |
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Numerical Size | 00 | 0-2 | 4-6 | 8-10 | 12-14 | 16 | 18 | 20-22 | 24-26 | 0 | 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 22 | 24 | 26 |
Bust | 31 | 32-33 | 34-35 | 36-37 | 38.5-40 | 41-42.5 | 43-45 | 47-49 | 51-53 | 32 | 33 | 34 | 35 | 36 | 37 | 38.5 | 40 | 42.5 | 45 | 47 | 49 | 51 | 53 |
Sleeve Length | 29.5 | 30 | 30.5 | 31 | 31.5 | 32 | 32.5 | 33.5 | 34.5 | 30 | 30 | 30.5 | 30.5 | 31 | 31 | 31.5 | 31.5 | 32 | 32.5 | 33.5 | 33.5 | 34.5 | 34.5 |
Waist | 24.5 | 25.5-26.5 | 27.5-28.5 | 29.5-30.5 | 32-33.5 | 34.5-36.5 | 37.5-39.5 | 40.5-42.5 | 44.5-46.5 | 25.5 | 26.5 | 27.5 | 28.5 | 29.5 | 30.5 | 32 | 33.5 | 36 | 38.5 | 40.5 | 42.5 | 44.5 | 46.5 |
Hip | 34 | 35-36 | 37-38 | 39-40 | 41.5-43 | 44-46 | 47-49 | 50-52 | 54-56 | 35 | 36 | 37 | 38 | 39 | 40 | 41.5 | 43 | 45.5 | 48 | 50 | 52 | 54 | 56 |
Inseam | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 | 31 |
Measurements are stated in inches unless otherwise indicated. Size chart values represent body measurements, not garment measurements. Some women's pants are available in petite and tall sizes. Typically petite sizes fit women 4'11" to 5'3". Regular sizes fit women 5'4" to 5'8". Tall sizes fit women 5'9" to 5'11".
PETITE: Generally, as compared to regular sizes, petite sizes are 2.5 inches shorter in inseam, 1 inch shorter in body length, 1.25 inches shorter in sleeve length and Âľ inch shorter in total rise.
TALL: tall sizes are 3 inches longer in inseam, 2 inches longer in body length, 2.5 inches longer in sleeve length and 1.25 inches longer in total rise.
Capri or cropped pants have an intentionally shorter inseam—reference the technical specs instead of this chart.
Inseam is measured to the floor.
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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This is my new favorite first layer. I’ve been wearing it everyday, that’s how great it is! PROS lightweight Soft Warm Partial zip at neckline CONS The only con for me is that it needs special wash instructions/guidelines - but this is true for all 100% Merino Wool clothing, and it’s worth it for how warm and light the garment is!
Fabric is great! It's extremely well made. It's a great base layer and keeps me very warm. I'd like to see what other colors this is available in. I received a black one which is not a color I usually wear. It is fitted, which makes sense for a base layer. I usually prefer a little looser fit.
I received this as part of the REI trailblazer program. The one I got is black (you may want to order a different color if you have light colored pet friends at home). The fabric is nice and soft and it feels lighter than I expected. The medium fits great (5'5", 150lb). I love the thumb holes and the sleeves are the right length. I like that the bottom has some curve to the front and back. This top will get a lot of use this coming ski season. I love merino wool. Thanks REI
This is a functional and affordable option for a merino wool long underwear top. When I first received the shirt it felt slightly itchy. After washing it the itchiness seemed to go away. I wore it for an all day work site visit on a rainy chilly day and it kept me perfectly warm. I like that it has a printed tag at the neck in place of a potentially itchy tag. It is a performance fit without feeling like a sausage casing.
I really like this pullover. It’s a great fit for a base layer, and the thumb hole is a nice touch. I like my sleeves to be long enough to cover a bit of my hands with multiple layers and this one worked great. I can’t think of a con! I got black, and the wool feels great. I normally wear a small and I felt it was true to size. It will be a staple for the cooler months—unless my sister steals it from me, she already has her eye on it :) pretty much a perfect base layer!!!
I love this layer. It’s mid weight but perfect for me—I run a little cooler and appreciate the extra warmth without the bulk. I have worn it hiking and around town under a vest. Have also worn it this weekend under a ski bib. All of the times I have felt comfortable, not too hot. Fit is true to size and meant to be fitted (5’4” 120#, got XS). Washed as directed and it didn’t shrink. Washes up pretty well. I do have to be mindful to wash this separately from my other laundry because I would be really upset if it shrank! Was not itchy at all. I prefer the half zip styles and this zipper was smooth, can be managed with one hand both ways (you know, in case you needed to breathe and didn’t want to take off both mittens). And the thumbholes are always a bonus!
I received this as part of the REI trailblazer program. The one I got is black. The fabric is nice and soft and it feels lighter than I expected. The medium fits great (5'5", 150lb). I love the thumb holes and the sleeves are the right length. I like that the bottom has some curve to the front and back. This top will get a lot of use this coming ski season. I love merino wool. Thanks REI
I hesitated to buy a S, because i'm on the fence according to the size chart between S and M. But the best color was only in S. I got it. It's HUGE. I mean, it fits me like I imagine an L *should* fit me. And it weirdly buckles in the chest area around the zipper. I had intended this to be something that when I went inside I could strip off other layers and look good, but it fits so weirdly (and is so oversized) that it has to be hidden under others layers. However, it is warm and the color is lovely.
I love this top. I’ve had similar quarter-zip merino shirts made by other companies, and this one is much softer. I have worn it to work, as a midlayer commuting in cold weather, and trekking. If I could give it more stars I would.
This is a great shirt for someone who looks great in ORANGE, burnt ORANGE. The color is very far from red. I don't live near sequoia trees, if I did I would know "sequoia red" is ORANGE. I wanted a red shirt to wear in the woods so hunters could see me, this ORANGE might as well be camouflage here in SC in the fall. Everything else about this shirt, the weight, the sizing, the neck, the hem is perfect. I don't look good in this color, and it won't help me stand out in the woods. It's ORANGE. If it had been described as fall oak leaf, I would have known it was ORANGE!