How to Choose Base Layers

A synthetic base layer for moderate temps, the men's REI Co-op Lightweight Long-Sleeve Crew keeps you dry and comfortable whether you're venturing into the mountains or trekking across open desert.
Imported.
View all REI Co-op Men's Base Layer TopsBest Use | Multisport |
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Shirt Type | T-shirt |
Fabric | 94% recycled polyester/6% spandex (bluesign approved) |
Sun-Protective Fabric | Yes |
UPF Rating | 50+ |
Moisture Wicking | Yes |
Quick Drying | Yes |
Underwear Weight | Lightweight |
Sleeve Length | Long Sleeve |
Gender | Men's |
Sustainability | Contains materials that meet the bluesign® criteria Contains recycled materials Fair Trade Certified™ factory From a Climate Label Certified brand |
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 | |
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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 |
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.
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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REI Product Advisor Review REI Co-op Lightweight Long-Sleeve Crew Base Layer Top - Men's | Black | XXL I am a REI Trailblazer, a Product Advisor for REI, and received from them a free, REI Co-op Lightweight Long-Sleeve Crew Base Layer Top - Men's | Black | XXL, in exchange for my honest review. They send us examples of current and potential product lines to test and review. We get to keep them when we’re done. Here is my review. I cannot recommend this top. If I had encountered it on a sales rack I would have walked past. On to the next. I was confused on the size. I saw that it was an XXL, but it appeared in the selection process that I could get it in medium. I take responsibility for that error. You’ll see in the pictures that I swim in it. I am giving it two stars out of five and not one star only because the construction is good. The seams are flat and look sturdy. They don’t feel abrasive, which could lead to abrasions if they were. I don’t think this top is at risk of falling apart during normal use. TBS, what I dislike about this top is the fabric from which it is made. While quality technical fabrics are much preferred over cotton and I do recommend for anything from running to backpacking, this fabric is not a quality technical fabric. The fabric of this top is made of 94% polyester and 6% spandex. To paraphrase the late Johnny Carson, a lot of polyesters died to make this top. The only reason the fabric might breathe at all is because it is woven and has the holes of woven material. The first thing I felt putting it on was hot and clammy. Wearing this top with this fabric is guaranteed to make you stink from built up bacteria, the kind which requires special soaps to wash out. The fabric is very much like that used to make the cheap tech shirt you get at some 5K foot races, the ones that end up being souvenirs you throw in a box and never wear, only to donate to Goodwill when you need the space. Honestly, that’s exactly where this one will go.
This shirt is a great choice for outdoor workouts. It's lightweight, breathable, and wicks moisture well, keeping you cool and comfortable on sunny days. The athletic fit allows easy movement without feeling tight, and the fabric offers good sun protection. The design is simple and sleek, making it easy to pair with any workout gear. It holds up well during activity and feels durable. Verdict: Comfortable, functional, and stylish — ideal for walking, running, or hiking.
This top has been a solid addition to my gear. The fit is comfortable and not too tight, but still functional for moisture-wicking. It's lightweight and breathable, perfect for layering or wearing on its own. I wore it in temperatures from the mid-30s to mid-60s, and it kept me comfortable during runs, hikes, and even while framing my basement. The fabric dries quickly and doesn’t feel heavy, even after intense activities. It’s also got a simple, minimalistic design that I appreciate, though the material can snag a bit on rough surfaces. Overall, it’s a great base layer for varying conditions, and I’ve been very happy with its performance. 5’11” 210lbs wearing size large in photo.
I had the opportunity to use this shirt on a car camping trip followed by an impromptu 50 mile gravel bike ride and it impressed me. It was reasonable warm when waking up with temps in the mid 50s F (but still comfortable to sleep in) yet did a great job of regulating my temperature while riding in the warm sun where it was hitting low 70s by the end of the ride. This was all the more impressive to me considering I was using the black version of the shirt! I'm 6' around 160 lbs with somewhat of a slender upper body (aka a road cyclist's body) and found the medium to be comfortable fit wise. Certainly not skin tight but not too baggy either. As a true base layer you may want something a little bit more form fitting but for how I use it the level of looseness was perfect and I don't think I would opt for a small. Overall this will become a stable of my outdoor wardrobe as the weather starts to turn cooler again into the fall and winter!
Needed to supplement my lighter layers. Found this at REI and it is an almost exact duplicate of a Patagonia layer I've owned for several years. Excellent quality, excellent price. What more could you ask for!