Reviews You Can Rely On

How We Tested Long Underwears

Tuesday October 12, 2021

By combining field experiences — like skiing down dormant volcanoes, sleeping through frosty desert nights, and running on snowy mountain trails — with specific lab testing designed to objectively analyze vital metrics, we work to create a comprehensive review process to rank these products side-by-side. This process allows us to note how well each pair of bottoms perform through a wide range of activities and environments, and then either support or contradict those findings with in-house testing. Below we break down how we test for each of the four metrics that make up the basis of our long underwear review.

Lots of field time, combined with calculated testing in the lab, is...
Lots of field time, combined with calculated testing in the lab, is the secret recipe to us providing you with in-depth articles to help improve your purchase power.
Photo: Jill Rice


We test for this factor just as any logical person would — we wear them in cold conditions, both alone as well as part of a layered system, and we make notes on how comfortable they kept us in varying levels of cold. We don these bottoms a stand-alone layer while shoveling the driveway, or out on early-morning runs in the chill of fall. We layered up to stand at the summit of Mt. Hood with sub-freezing winds, for sleeping while backpacking through the high-alpine environments of New Mexico, and for gathering around bonfires with friends on chilly nights.

Just below the howling winds atop the summit of Mt. Hood on a winter...
Just below the howling winds atop the summit of Mt. Hood on a winter ascent.
Photo: Roland Mott


In the field, we tested breathability by pushing ourselves to work up a sweat in a myriad of environments and temperature ranges — from pre-dawn skinning in sub-freezing temperatures, to trail-running in the hills outside of Salt Lake and Santa Fe. In the lab, we conduct a more controlled breathability trial to support our field testing. In a temperature-controlled environment, we go through a highly aerobic, body-weight workout. Testing each pair of bottoms side-by-side, we go through a quick routine of push-ups, pull-ups, burpees, jump squats, and mountain climbers. We note how much sweat we worked up to judge general breathability, how well that particular layer did in terms of wicking away sweat, and then timing how long it takes for our skin to dry. All of this together helps us build an assessment of how well each pair will dry off on the body while pushing through vigorous activity.

Lightweight, synthetic options tend to be highly breathable and...
Lightweight, synthetic options tend to be highly breathable and quick-drying, and versatile enough in terms of thermoregulation to carry you through 3-seasons of outdoor playtime.
Photo: Jill Rice

Drying Speed

In addition to our on-body assessments of drying speed, we fully saturate each pair of bottoms and then hang them to record air-dry times. We note how long it takes for the face fabric to dry, and how long for the entire garment to dry all the way through. By comparing these bottoms side-by-side, we are able to gather some more objective information about how efficiently individual fabrics or fabric purge moisture. It is important to know that saturated hang-dry times do not exactly reflect the garments ability to wick away sweat, the most important factor in terms of keeping you dry during activity. Some fabric types — especially Merino wool — typically have slow hang dry times when the fibers are soaked all the way through, but do an excellent job of staying dry on your body. But it does give us an objective way to test how quickly a face fabric evaporates moisture, or how quickly a layer may dry out if you're washing and laying it flat to dry on a rock during a backpacking trip.

After 4,000 vertical feet of skinning, you know whether or not a...
After 4,000 vertical feet of skinning, you know whether or not a pair of bottoms are breathable. Winter ascent of Mt. Hood, OR.
Photo: Roland Mott

Comfort & Fit

This metric is tested by wearing these bottoms while we're out playing, and making lots of notes on how the features fit, how comfortable each pair feels, and how all of this works together to support garment performance. A few examples of things that we don't want to see in a pair of long underwear are: the waistband tends to stretch out over time; this pair is really tight through the calves or cuffs; the crotch sag on this one is really awkward, and uncomfortably bunches when layering. Through careful observation and close scrutiny of details, we analyze each bottom to see how they compare relative to one another. Some factors that contribute to our assessment of comfort are: how enjoyable they are wearing next-to-skin; the comfort and fit of the waistband; their ability to layer smoothly; and any particular observations that result in the bottoms feeling uncomfortable or awkward. While 100% Merino wool layers are often the plushest, we try to remain objective in our evaluation of this inherently subjective metric — we've noticed that in recent years, 100% recycled polyester is giving the all-natural fibers a run-for-their-money when it comes to next-to-skin comfort.

The waistband is a starting point when considering the comfort of...
The waistband is a starting point when considering the comfort of any quality pair of long underwear, and not all waistbands are created equal.
Photo: Jill Rice

Fit is a more detailed investigation into how the garment is designed, and how that translates into how it wears on the body. Factors such as seam patterns and articulation, the length of legs and tightness of the cuffs, the cut of the seat and crotch, ease of fly access, how well the bottoms stretch and move with you, and any additional features or thoughtful touches that may contribute to a remarkable fit. Through careful analysis in the lab of their design and many notes taken during many hours of field testing, we hope to paint a pretty sophisticated picture of how each pair of bottoms may fit.

As with all clothing — but particularly with the investment of technical clothing — we can't stress enough how important it is to visit your local shop to check these products out for yourself. We all have different wants and needs in terms of the perfect fit for our bodies. While we do our best at OutdoorGearLab to consider all of the fit-factors, we're still limited by what our testers experience in their own bodies. A picture may be worth a thousand words, but hands-on experience is worth a thousand more.

Maximum articulation may factor heavily into freedom of movement...
Maximum articulation may factor heavily into freedom of movement, but the layers with exceptional engineering are not always the most comfortable.
Photo: Jill Rice


Outside of living in these bottoms and dragging them along on our climbing, skiing, running, rafting, and hiking adventures, to objectively test durability we also conduct a controlled test in the lab that measures the durability of the face-fabric against abrasion. We grind the knees of the fabric a set amount of times across an 8-inch distance of gritty granite to see how the fabric fairs (think washing board technique.) This may seem overly aggressive when compared to likely real-world applications, but this specific test gives us a very clear idea of how each bottom holds up to abrasion. While some layers only develop a bit of surface wear, others develop holes immediately. We also send them through a relentless amount of machine wash and dry cycles — a great indicator of realistic product life.

Results for our merciless abrasion test.
Results for our merciless abrasion test.
Photo: Roland Mott