Smartwool Merino 250 Bottoms - Women's Review

The Merino 250 is a merino wool base layer that kept us warm on the coldest of adventures. When layered underneath breathable pants, it dries quickly, keeping you dry even when you sweat. After testing these long underwear bottoms for over three years, we are happy to report their one of the warmest layers that we tested, however, we're disappointed in their overall durability.

Performance Comparison

The Smartwool 250 will keep you warm whether you're riding the chairlift or taking advantage of the warmth generated from the sun during the unpredictable change of season.

Credit: Toby Swimmer

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 also offers a great range of thermoregulation. We recommend the Smartwool 250 Bottoms if you tend to run cold or prefer a thicker base layer to keep you warm even in the depth of winter.

We've had the opportunity to test this base layer for a few years, thanks to the updates and improvements from Smartwool. 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 as well as efficient thermoregulation.

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

Credit: Amber King

Sitting on a cold chair lift for 15+ minutes in Telluride, Colorado with a simple shell over these bottoms 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.

The thicker wool construction offers stretch and breathability, while the Merino wool fibers are able to maintain 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 kept moisture off our legs, keeping us dry. After opening up the vents, the base layer dries out very quickly, which inevitably leads to better warmth all day long.

Breathability

While this base layer bottom is breathable, we would recommend wearing this bottom on colder days where you need more insulation and less of a wicking layer. While it can certainly breathe, the fabric tends to hold more moisture without appropriate ventilation from a pant above. On its own, the fabric stays dry, no matter how sweaty you get. However, given that it looks like long underwear, it's not our first choice to wear on its own when out in public.

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

When running, ice climbing, and hiking, we noticed that the pant got sweaty and stayed a little wet if we didn't open up the vents on our ski pants while skinning uphill. The lack of ventilation in these leggings made us prone to overheating during activity and for this reason, we would recommend a synthetic option or a merino base layer with ventilation panels that offer a more efficient drying speed that will increase your level of warmth during activity.

Here we wear the Merino 250's on an ice climb in the Ouray Ice Park. They offer good breathability in motion when vented properly.

Credit: Amber King

However, when we took these bottoms on a winter run/hike way up in the snowy San Juan Mountains, we weren't completely disappointed by its performance. This trail was filled with post-holing opportunities, rocks, mud, and just under 4,000 feet of vertical gain while descending along a 10-mile path. While this pant was able to perform in these conditions, we would recommend a more breathable merino option for maximum comfort during strenuous activity.

While this layer does not perform as well when other layers on top prevent proper ventilation, we noticed its ability to keep the snow off our legs and dry quickly when exposed to air while worn on its own.

Comfort and Fit

Merino wool is super cozy and soft to the touch. While the 100% merino wool construction of these pants offers more comfort than synthetic options, it is not the most comfortable merino layer that we tested. However, it is comfortable enough to be worn all day during a variety of activities.

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. We wore it on several trips where it was our only layer for weeks. 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.

The fit is regular with both full-length and ¾ length options available. In terms of fit, we are pleased with the new update. In the past, the butt of these pants sagged severely after just a few days of wear. 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 and the size is true to fit.

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 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 pant is best when utilized underneath another layer with proper ventilation to prevent overheating and moisture build-up.

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 but we still recommend using caution when wearing on its own due to the soft nature of the material that is prone to snag.

As a thicker base layer bottom, there is a little more durability in the wear of the face fabric, simply because there is more fabric 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 them 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 warm and happy in the Smartwool Merino 250.

Credit: Amber King

When taking it with us running and hiking (without an overlayer), we found that the fabric snagged more than any other layer. We also noticed that the material does pill after a few washes, but this doesn't change its ability to thermoregulate. While Smartwool has improved the durability of these bottoms over the years, we still got holes in the knees after snagging nails in a boat which we would imagine being the case with most layers in that situation.

The welded seams made us question their durability, we much prefer the flat lock seams these bottoms feature below the waistband.

Credit: Toby Swimmer

Value

While this layer is a good option for warmth due to its thicker merino fabric, we would expect more durability when worn on its own. If you tend to run warm, there are lighter options available for less money upfront. All in all, this is a solid layer but we would recommend other merino wool options that will give you more years of wear and tear for your investment.

When rain keeps you from climbing at Cat Wall, the Smartwool 250 bottoms will keep you comfortable during your training run.

Credit: Toby Swimmer

Conclusion