The Midweight base layer is a very affordable and top-performing base layer tested. Wear it all year while relishing in its exceptional breathability, style, and fit.
Performance Comparison

The Midweight Base Layer is notable for its low price and fine performance.
Photo: Amber King
Warmth
As a thinner synthetic base layer option, it certainly is not the warmest of all the contenders. Featuring a 92% polyester/8% spandex blend, it performs well to wick away moisture and keep your skin dry. However, the material is not the greatest at allowing for the evaporation of moisture and instead holds moisture in the fabric if it is supremely wet or humid outside.

This top is a little thinner than most and as a result, it's not the warmest in this review. That said, it does well as a base layer in colder weather.
Photo: Amber King
We tested this piece while backcountry skiing through the winter and hiking in the winter. As a stand-alone piece, the fabric is super thin and provides great thermoregulation to dump heat. That said, in the winter, it is not our top choice for super cold days as the material simply doesn't insulate as well as other layers with a fleece-lined interior or a merino wool construct. That said, it performed superbly for aerobic activities in cold weather. Overall, great for active cold-weather wear but not a fantastic option to wear if you're going to be sitting around in the cold in the Arctic.
This top is also available in the REI Co-op Midweight Base Layer Half-Zip. This top can add a little extra warmth by covering up the neck.
Breathability
If breathability is what you seek, it provides! In all things outdoorsy, it performs quite well keeping you warm and mostly dry in a wide range of temperatures. The polyester blend is tight-fitting, wicking away moisture from the skin in temperatures ranging from zero to 50 degrees. The material is thinner and somewhat porous, allowing air and moisture to move readily. That said, it doesn't breathe well in all conditions.

The crew collar of the Midweight base layer is perfect for snow hiking on warmer days.
Photo: Jordan Erlenbach
While it works well in warmer temperatures, we found that when layering it under a mid-layer, the fabric wicks, but doesn't readily evaporate well. When ski touring on a cold day, when wearing this base layer on its own, we were comfortable and dry. However, when the wind picked up, we added a mid-layer, and it stopped breathing as readily. It still managed to wick moisture away, however it seemingly got trapped in the fabric. When stopping to eat a sandwich, we noticed our core temperature dropping. The fabric was colder than other options out there sadly. As a result, we wouldn't recommend it as a layer to wear in super cold temperature where you might have to sit around for long periods of time after sweating. But it does a great job during warmer runs or hikes as a stand-alone piece.
Comfort & Fit
We adore the comfort of this contender. Our testers love the stretchiness of the thinner fabric and its stretchy, longer fit through the torso and arms. It is simple and well crafted. While layering it under fleecy layers, the shirt stays in place and conforms to the curves and shoulders of even our more voluptuous testers. It hugs thinner frames and provides great coverage for all body types. It is true to its size.

A look at the fit of this comfortable synthetic base layer.
Photo: Amber King
While the face fabric is soft to the touch, it's not as cozy or comfortable as merino wool contenders. The fabric also feels great against the skin, without itching when it gets wet or sweaty. Overall, this comfortable bare-bones baselayer is excellent for wear-all-day or multiple days on end.
Layering Ability
Featuring a slippery face fabric and thinner construct, this top is easy to put underneath fleece mid-layers or jackets. The fit is tight to the skin, so it doesn't bunch up or catch when pulling layers over on top. Because of its tight fit, though, it's not ideal to put a t-shirt underneath. Only a tight tank top will fit readily. Overall, it's easy to layer.

Trying on different layers in double negative digits in Northern Ontario.
Photo: Shawnn Row
Durability
With over three months of testing and over 15 washes, durability is a non-issue. We took it running, climbing, and skiing, wearing it with heavy (and light) backpacks in a wide range of temperatures. Through it all, it shows little to no wear and tear! We didn't observe any pilling or stitching fly-aways. The burly polyester fabric provides resistance to high-friction sports like crack climbing and canyoneering. Our only caveat in this category is the fabric (despite the odor-resistance) started to retain a stench after this period and pills after a few uses.

This layer proved to be fairly durable, except there was minor pilling observed at the seams.
Photo: Amber King
Value
We think this base layer is of high value. It has a low price and is a durable product. It will keep you happy for years to come. We appreciate a low price tag for a product category that undoubtedly won't last as long as other gear purchases.

Take this layer winter exploring or on your next adventure into the backcountry.
Photo: Shawnn Row
Conclusion
This budget-friendly option will have you charging uphill in the snow, spring, and fall. Wear it as a stand-alone piece in the winter or under a cozy mid-layer in the winter. For a great
low price, the durable
REI Co-op Midweight Crew is a great synthetic option.