Smartwool Merino 250 Bottoms - Women's Review

The Merino 250 is a merino wool base layer with the construction that'll keep you warm on the coldest of adventures. When layered underneath a breathable paint, it dries quickly, keeping you dry even when you sweat. With the broadest range of thermoregulation that we've seen, it wins our Editors' Choice Award. Testing it for over three years, it's been reliable and has kept up its performance, even though we've put a few holes in the knees.

Performance Comparison

Our Editors' Choice winner is easily layered and provides an exceptional range of thermoregulation. Warm and breathable, it'll keep you cozy and dry even on the sweatiest of adventures.

Warmth

Loaded with 250-grams of merino wool, these long underwear bottoms are some of the warmest that we've tested over the last few years. It offers the widest range of thermoregulation. If you run cold or prefer thicker base layers, this is our top recommendation.

With the last few updates from Smartwool, we've had the opportunity to test this base layer for a few years. We've worn it while tackling all sorts of crazy missions across the world. We've taken it ski touring in Alaska, sailing in the Faroe Islands, running in the Peruvian Mountains, and resort skiing in Colorado. Through all these cold-weather activities, it's provided sufficient warmth by offering good insulation and comfort against the skin, while thermoregulating like a pro.

Here we test the Smartwool 250 on a winter hike in the Colorado mountains.

Sitting on a cold chair lift for 15+ minutes in Telluride, Colorado with a simple shell of pant is a great way to test for insulating warmth. In this situation on the coldest days, yes, we got a little cold, as anybody would while sitting still for this long in cold weather. However, in comparison to any other long underwear bottom in this review, it offers the best insulation, especially when worn with uninsulated pants.

A look at the thicker fabrics that offer much warmth, especially in cold weather.

The thicker wool construction offers nice stretch and breathability, while the Merino wool fibers do great work at holding heat when you aren't moving. After sitting on the chair lift, we'd pop off and start skiing swiftly through the trees, building up a sweat. Even without vents open on the pant, this layer did good work to keep moisture off our legs, keeping us dry. When we opened up the vents, the base layer dries out very quickly. This inevitably leads to better warmth all day long.

Breathability

This base layer bottom is quite breathable, keeping you dry, even when energy output is high. We would choose to wear this bottom on colder days where you need more insulation and less of a wicking layer. While it can certainly breathe, the fabric can hold more moisture without appropriate ventilation from a pant above. Luckily, it dries quickly once ventilation is received. On its own, the fabric stays dry, no matter how sweaty you get. However, given that it looks like long underwear, it's not the first choice to wear on its own out in public.

Like any great merino wool product, the Merino 250 offers wonderful breathability and wicking ability. The super-soft fibers are great at grabbing moisture that might be sitting next to the sweatier parts of your legs, absorbs it, then transfers it out to the exterior environment, when given appropriate ventilation.

Here we test the Smartwool 250 on a snowy ridge climb in the San Juan mountains. We run/hike up 4,000 feet to get to a summit as 12,000 feet. These pants offer great warmth and kept us dry, even when sweating and picking up snow around our ankles.

When running, ice climbing, and hiking, we noticed that the pant only got sweaty and stayed a little wet if we didn't open up our ski pants while hiking uphill. As soon as we vented the fabrics, the moisture immediately left the area, drying quickly. Of the different pants we've tested, all merino products performed to a similar level. Synthetics offer great drying speed, but for some reason, the moisture feels like it would linger a little longer in the fabric than merino products like this one.

Here we wear the Merino 250's on an ice climb in the Ouray Ice Park. They offer good breathability while in motion and when it's our turn to belay.

When we took this pant on a winter run/hike way up in the snowy San Juan mountains, we were pleased by its performance. This trail was filled with post-holing opportunities, rocks, mud, and just under 4,000 feet of vertical climbing and descending along a 10-mile path. While this pant is not one we'd typically choose for this trail, we were surprised at its performance. It kept us warm and dry the whole time.

The fabric does a great job of beading up water and snow. While the fabric does eventually absorb the water, it dries quickly when exposed to the air. Another reason we love this base layer.

When post-holing, the merino wool kept the snow off of our legs. Even when the water did absorb into the fabric, it dried within minutes of running. After our run, we kept the pants on while hitting a local pizza shop and while watching a movie at home afterward. The fabrics stayed dry and warm through all of it! A highly recommended piece for cool to cold days in the mountains.

The Smartwool 250 offers good sun protection and insulation on this sunny day backpacking into the Grand Canyon.

Comfort and Fit

Merino wool is super cozy and soft to the touch. In these pants, it feels comfortable against the skin. As we just mentioned before, this is a pant that you can truly wear all day, from the trail and back into bed.

Merino wool is not an itchy fiber. Spun from the wool of merino sheep, now found in many places in the world, it is biodegradable, organic, offers natural UPF protection, and is super soft. The thicker construction of this pant offers amazing comfort that'll last for however long you wear it. We wore it on several trips where it was our only layer for weeks. In fact, when sailing in on the North Sea, this is what we wore underneath all of our raingear. After two weeks of not washing it (we know…gross), it didn't stink, even after being next to our skin the entire time.

While hiking to the highest sea cliff in the world, we wear a comfortable pair of base layer bottoms that'll take us from the trail and into our sleeping bags, without needing to change. We chose the Smartwool Merino 250 for this particular mission. Especially when there's two sunrises to watch at 1am at a high latitude of the Northern Hemisphere.

The fit is regular with both full length and ¾ length options available. In terms of fit, we are very happy with the new update. In the past, the butt of these pants sagged severely after just a few uses. The latest version fixes this issue by adding a new seam. Yes, it does stretch a little after a use or two, but it holds its shape for the most part. The size is true to fit.

A look at the overall fit of these super comfortable base layer bottoms.

Layering is also easy, but be sure the pant you put above it has a little room. The thickness of the fabric isn't the best for your skinny jeans, but it works nicely underneath a pair of work pants, snow pants, or soft pants. The face fabric is a little grabby, so if the above pant is fleece-lined and tight, you might have to work a bit harder than you would with a tight synthetic layer to get it on. Overall, this is a super comfortable pant that is best used underneath another layer, be it a pair of shorts or pants, or for lounging around at home.

The uber thick waistband offers all-day-long comfort while the flat seams avoid any kind of chaffing, especially in cold weather.

Durability

After many years of use, we are surprised at the overall construction and quality of these base layers. The durability is good, but not the best that we've ever seen. After many years of use, it's still holding up. The newest version that we've tested has been in hard use for the last few months, and still looks great!

As a thicker base layer bottom, there is a little more durability in the wear of the face fabric, simply because there is more to wear through. However, this pant has longer fibers that grab easily when being brushed against things like plants or bushes, which is why we recommend using it with another layer. The face fabric doesn't have a tightly-knit configuration that is super durable or slippery like other merino-synthetic blends or synthetic bottoms.

An awesome layer will hold up underneath a pair of pants while biking, backpacking, and more. Here we hike to a lake above an ocean in the Faroe Islands, an island cluster belonging to Denmark, in the North Sea. Ida is stoked! Despite cold rainy weather, we are warm and happy in the Merino 250 by Smartwool.

When taking it with us running and hiking (without an overlayer), we found that the fabric snagged more than any other layer. Underneath a pair of pants, they are great. The material does pill after a few washes, but this doesn't change its ability to thermoregulate. While we did observe some thread fly-aways, these aren't red flags, and we believe this bottom is well-crafted. Especially when we've had a previous version of this layer for several years. Aside from just a couple of holes in the knees (from snags on a nail in a boat), it is still going strong.

While the fibers are more susceptible to wear and tear as they are thicker and 'grabbier' they are still pretty durable. Even though we've only tested this version since it came out in 2019, we've been testing previous iterations of this product for over three years, and it continues to perform well for us.

Value

While the initial investment might seem high for a pair of long underwear, this price is definitely worth it. If you're in the market for a warmer long underwear bottom that'll thermoregulate while you play in colder weather, this is a great choice. For those that run warm, take a look at the lighter options that are also much more inexpensive. There is a lot of value in this bomber base layer.

Find solace and confidence with the Smartwool 250 Merino base layer bottom. It'll keep you warm and dry.

Conclusion

The women's Smartwool Merino 250 is a midweight long underwear bottom that offers the widest range of thermoregulation we've seen. Underneath a pair of pants, it'll keep you nice and toasty in the winter, even when you start to sweat. In the summer, it's a great layer to bring for colder summer nights in the tent. Looking a lot like long underwear with a less durable build when worn on its own, it's not our top choice for wear-alone use. But if you prefer warmer base layers, instead of thinner ones, this is our best recommendation.