The REI Co-op Lightweight Bottoms are a well-designed synthetic pair of long underwear that offer simple function at an unbeatable price point, earning our Best Buy Award. As a lightweight pair, they aren't our recommendation for bitterly cold activities like snow camping or ice-fishing. But, for active pursuits in cold weather, they work just fine! We found that these also hit their stride in Fall and early Spring, when you're looking for a little extra warmth to layer with. Thanks to near top-notch breathability — and an infusion of spandex — these worked great as a pair of running leggings, or a quick-drying pair of bottoms to take on a backpacking trip.
REI Co-op Lightweight Bottoms Review
Cons: Short cut legs, average comfort and warmth
Manufacturer: REI Co-op
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Our Analysis and Test Results
A simple, synthetic pair of long underwear to get you outside in colder weather, the REI Lightweight bottoms are everything we expect out of a well-designed workhorse of a base layer. These bottoms are nothing spectacular — instead they are a quality product at an unbeatable price-point. As one of the lightest-weight options included in our review, we did not expect them to be a top performer in terms of warmth. But they did shine with regard to breathability, scoring near the top-of-the-charts. These are a great, everyday option for running leggings, especially with the addition of spandex for a little added stretch.
The smooth, almost silk-like face fabric — combined with a snug, athletic cut — made these bottoms incredibly easy to layer over, even under everyday pants. We often layered up with these for chilly mornings of farm work, when we needed a little extra heat to get through the first few hours, but knew that we would still be comfortable when temperatures rose later in the day.
As a lightweight, 100% polyester option, these simply will not keep your legs as warm as a midweight, wool base layer. The material is crafted to keep you just warm enough until you work up a sweat, and then maintain a dry, consistent environment so that your legs don't end up as soggy-popsicles by the end of the day.
The fact that these REI bottoms are designed with a UPF 50+ sun protection should give you some clue about their intended purpose — slide these on as a base layer under shorts on a backpacking trip, or as cool-weather running leggings.
Lightweight pairs of long underwear are designed to perform through the other three, non-snowy seasons. We were very comfortable sleeping in these bottoms on alpine nights through the summer, even with temperatures dropping into the mid-40's. One of our testers has worn this pair throughout northern California winters on backcountry and resort ski days for the last two years. These base layer bottoms do fall short in the warmth department during sedentary activities in the depths of winter, though.
The metric that is the shining light for this layer, the REI Lightweight bottoms can hang with the best of them when it comes to breathability. By their nature of design, we expect lightweight options to afford the highest levels of breathability, and these perform right in line with this expectation. These almost silk-weight bottoms are cool to the touch, and are dappled with ventilation pockets.
This pair of long underwear is great at dumping heat when our heart gets pumping. A majority polyester build, these bottoms actively dry off on our bodies — and thanks to the infusion of spandex, maintain their form fit even after a long day of soaking up sweat. While it was a little chilly to step out in these on our early-morning runs in the fall, once we got moving, the REI Lightweight bottoms proved themselves as a solid option for running leggings.
Comfort and Fit
It's tough to compete head-to-head with full-Merino when it comes to comfort — we don't like to judge synthetics right off the bat, but often we find that a polyester layer really needs that wow-factor to stay in the ring with their all-natural competitors. Despite the somewhat sticky feel of the material in your hands, the REI lightweight bottoms are surprisingly smooth next-to-skin. By incorporating 8% spandex into the otherwise full-polyester knit, these bottoms are stretchy, with almost a silk-like feel.
These bottoms are fine regarding comfort, but have a few minor drawbacks. The flatlock seams are slightly bulkier than other full-synthetic options we tested. There are other points, particularly through the seat of the pants, that would randomly poke and scratch us throughout the day's activity if worn bare-bottom. But simply pulling on a pair of underwear — which layered just fine underneath these athletically cut bottoms — seemed to solve this minor problem. It would take the keenly discerning wearer to notice these things, though.
These do a good job of hugging the buttocks, and articulation through the crotch — combined with the stretch of the spandex — offers plenty of mobility. The main area where the REI lightweight bottoms lose points is in the legs and cuffs. The cut of the legs, despite being listed as a 32-inch inseam for a size Medium, stops a couple inches above the ankle on our lead tester. This left a skin gap that let in some cold air, unfortunately.
The ankle cuffs are not sewn with the same flat lock seams used throughout the rest of the pant, which make it uncomfortable to roll up when wearing ski boots — they constrict the calf, rather than stretching to accommodate the adjustment. Our testers preferred to leave these bottoms tucked into their ski boots for the sake of comfort.
The REI Lightweight bottoms will eventually fall victim to their thin construction when it comes to durability. These are one of the few bottoms that bore a hole after our abrasion test. While this test is certainly harsh, many other synthetic layers in our review held up significantly better than this pair. Objective durability tests can tell us a lot about a garment, but so can real-world use. One of our testers has exclusively used these bottoms for all his cold-weather activities (running, backcountry and downhill skiing, dog walking, snow shoveling, and more) for the last two winters without any significant wear and tear.
For some reason, the ventilation-hole pattern is knit into the outside-face fabric. While this adds to the impressive breathability of these bottoms, it does leave these small pockets of thinner material exposed to the harsh environment of rip-ready tree branches, thorns, and cactus if worn as an exposed layer. While we tend to avoid running through a patch of prickly pear, we found this worth noting.
Are you looking to upgrade from your dimpled, cotton long underwear of the past, but shocked by some of the prices of synthetic and merino wool layers? This model is simply a pair of long underwear designed to get the job done. Expect a reliable pair of bottoms that offer respectable warmth, with above-average breathability and comfort, that will serve as a workhorse through the colder seasons. Don't expect excellence — but do expect a quality product for an unbeatable price.
Everything you expect out of a lightweight base layer, the REI Lightweight Bottoms will not disappoint if you are looking for a versatile pair of long underwear. Our Best Buy Award winner for a reason, these offer solid performance at an unbeatable price. Pick these up so that you can continue your adventures into the colder months of the year — or even on those chilly nights when you need a little bit of extra warmth in the spring and summer.
— Roland Mott