REI Co-op Midweight Bottoms Review

The REI Midweight Bottoms came out top in warmth for a synthetic and not too far away from the heaviest wool base layers we've tested. They offer a great balance of warmth and breathability and also dry quickly. The four-way stretch fabric makes these a pleasure to wear, whether layering or not. But the real strengths of these bottoms are simply their amazing durability and fantastic price — especially when compared to a comparable wool layer. Probably one of the best-priced pairs of long johns when looking closely at performance, it's not a hard choice to add this layer to your cold-weather wardrobe.

Performance Comparison

Warmth

These are toasty! The Midweight Bottoms provide great warmth for their weight, only surpassed by much more expensive and slightly heavier wool options. For comparison, our lab tests put these synthetics in approximately the same warmth bracket as a 200 g/m² wool layer.

Generally, we suggest you don't wear too thick of long underwear, as it impedes comfort, fit, and breathability. Better to just put on an additional mid-layer if more warmth is needed. The Midweight Bottoms are a great example of a warm pair of synthetic bottoms that also have a great mix of breathability and comfort.

We tested these for warmth in a variety of situations, including climbing on Longs Peak in Rocky Mountain National Park during cold and windy conditions. We wore them under running tights and while sleeping underneath the stars. In both circumstances, the Midweight passed our warmth anticipations. We found the snug-but-not-tight fit works well with trapping heat and wicking moisture, doing nothing but making these bottoms feel even warmer.

Breathability

The Midweight Bottoms do a fine job keeping things breathable for their weight. Polyester-based long underwear like these usually perform exemplary in breathability, as the synthetic fabric naturally wicks away excess moisture from the surface of your skin. The snug fit also helps with breathability, aiding the wicking nature of the fabric by ensuring your skin is in contact with the fabric itself.

Keeping dry is important to keep comfortable — especially for long underwear. Changing out of a pair means taking off pants and shoes, which can take time. We're a bit impatient ourselves, so if we can keep comfortable, we'll often choose to keep them on until we get back to the trailhead, even though we may be getting a little toasty.

Comfort and Fit

The REI Midweight Bottoms are some of the comfiest synthetic pairs of long underwear we've had the pleasure of testing. The fabric is more smooth than ultra soft, but the four-way stretch really makes them feel wonderful to wear, allowing for great freedom of movement. Minimally obtrusive flatlock seams throughout keep pressure points out of the picture, and we were delighted to find that such a budget pair of midweight leggings still include a gusseted crotch, helping out with the bottom's already excellent articulation.

The cut of the Midweight is neither loose nor tight, and the four-way stretch fabric should allow for a wide spectrum of body types. The inseam is approximately 31" for a size medium and worked well for our main tester, who usually wears a pant with a 32" inseam; the bottom cuff rests just above the ankle. The 1.5" waistband is also approximately 31" around unstretched and didn't feel too tight for a 32" waist. There is a fly on the front for convenience, and the bottom cuffs are minimal, without any additional stretch built in.

Durability

The Midweight Bottoms are all but custom-made for the accident-prone, like our main tester who can't help but bump into trees and slip on ice. They are one of the burliest pairs we've tested, thanks to their midweight synthetic fabric and tight weave. Our harsh lab tests that usually leave most wool long underwear shredded resulted in only superficial damage to the REI Midweights.

In our real-world testing, we found no degradation to the comfortable four-way stretch, which hasn't lost its shape or elasticity. Tough, flatlock seams are found exclusively throughout the bottoms, and we noticed no premature wearing of these seams or of the fabric itself. The thick 1.5" waist strap has plenty of stretch and can take a fair amount of abuse. We would suggest following the manufacturer's recommendations of only drying on low, as there is elastane in the waistband and, if we were to guess, in the fabric itself.

Drying Speed

The Midweight Bottoms fared decently here. The synthetic fabric has a tight weave, and the fabric weight itself is the thickest of any of the synthetics that we've tested, so the results we gathered track. Drying times were faster than the thickest wool and wool blends we've tested, but this is also to be expected, as wool usually holds onto moisture a little more than synthetics.

Cross-referencing these findings with what we've seen with warmth and breathability would suggest to us that the REI Midweight Bottoms are best for colder outings, where you don't run into the issue of overheating and over-perspiring. Putting these to work while ski touring would be an excellent use case. Once at the hut, hang them up to dry near the fire, and they'll be perfectly dry for the next morning's laps up the adjacent hill. Unfortunately, these bottoms don't come with any odor control/antimicrobial technology, so there's a chance that they will start smelling a little ripe after a few uses between washes. We personally didn't experience anything overly offensive, which we're grateful for avoiding.

Layering Ability

The REI Midweight Bottoms are built to be social butterflies at the layering party. The smooth fabric works well when layering up with mid and top layers, as the material won't catch on other scratchier apparel. In our real-world tests, we paired the Midweight Bottoms with running tights, hiking pants, down pants, and our bedtime flannels without a problem. These bottoms are designed to be worn underneath another layer, as the presence of a front fly will attest. Not being an aggressive, athletically tight fit, you can wear a layer underneath the REI Midweight if you so desire — we regularly wore a pair of running shorts ourselves. That said, we would suggest them as a next-to-skin layer for most applications.

The fabric's four-way stretch also prevents the bottoms from bunching up in awkward and hard-to-reach ways, which is important for a mid-layer. Minimal cuffs at the ankle do their job in keeping the legs from riding up, and the midweight fabric didn't feel too bunchy when paired with a thick sock or clunky hiking boots. Stitching and seams are fairly minimal throughout these bottoms, and none are located in any problematic areas, like the crotch, which is gusseted to avoid such issues.

Should You Buy the REI Midweight Base Layer Bottoms?

If you want the best midweight synthetic long underwear that we've seen, this is it. The excellent price is just an added bonus — chances are that we'd give you the same recommendation if these leggings were twice the price. Their only real weakness — if you can even call it that, is their absolute warmth, given their weight. A wool or wool blend base layer would be just a little bit warmer. Unless you're counting grams for your next FKT attempt, these bottoms will keep you warm all season — and because they're so durable, for many seasons to come after that.

What Other Long Underwear Should You Consider?