Smartwool Merino 250 1/4 Zip - Women's Review

This top performer continues to prove itself in all conditions. The Smartwool Midweight ¼ zip is the one you want if warmth and comfort are your top priority. A heavier construction with the softest materials, warmest performance, and excellent thermoregulation. This is the layer to wear under a fleece and jacket in super cold weather or on its own when you start to shed your layers.

Performance Comparison

The Smartwool Merino 250 1/4 Zip is a favorite for its excellent fit and cozy materials. The cut is versatile, making it a great choice for a wide range of activities, whether you're lounging around town or skiing at the resort.

Photo: Amber King

Warmth

This base layer top is warm and offers excellent thermoregulation. If you're seeking a top that'll keep you warm when the temperatures plummet, this is our top recommendation. While it's advertised as a midweight construction, it's thicker than any other midweight contender, loaded with 250 g/m² of merino wool, making it exceptionally warm. We tested it across a wide range of temperatures, ranging from 0 to 75 degrees Fahrenheit.

During an exceptionally cold week in Colorado, we had the opportunity to test the warmth of this high performer. The thicker construction, when pulled on, immediately begins to insulate. The fine fibers hold heat but also release moisture. With its 100% merino wool construction, there's a little porosity in the material, which allows moisture to escape when moving, which ultimately keeps you warmer.

The length is ample through the arms, and torso length is ample and with a lot of stretch. When wearing it under a down vest, we were easily able to pull the arm cuffs over our hands when clouds came in, and we were without gloves. It offers full coverage with a thicker construction, making it an excellent cold-weather addition to your outdoor wardrobe. Trust it on any ski, hiking, bike mission in the winter. Or wear it on its own through the warmer season.

When we dip into canyons, the air began to crisp and chill. Luckily the thicker construction keeps us warm in these colder trenches. Oh...it does really well in a layered system, too.

Photo: Amber King

Breathability

Merino wool is known for its excellent breathability. The 100% merino construction of this top has a looser weave than other merino tops, making it surprisingly breathable right through the face fabric. The ¼ zip allows you to vent easily, making it more versatile than most crew base layer tops on the market. While this is a breathable base layer, it's far from our first choice for aerobic or sweaty sports during warm months because of its thicker construction. For this use, we'd opt for a thinner build.

During our testing, we took this top on many missions, from climbing to running. While running, we learned this top is best for colder days of the season. Depending on how warm you run, this may be best for winter, or it may work for you in the shoulder seasons. We prefer to use it for cold early morning runs.

The materials feel thick, but they are very breathable. The material is porous and allows easy airflow. The 1/4 zip offers more ventilation than a crew top, which makes it versatile for a slew of activities.

Photo: Amber King

During warm weather, we found ourselves keeping it on before really building up a sweat and having to strip it off. When wearing a backpack, we found the material retained and held sweat where breathability was poor with our outer layers. However, these wet spots still stayed warm, even when we cooled down. The materials also dry very quickly. Overall, this is a breathable but thick layer, doing best in cold or cool weather in a layered system. On its own, it'll do well for any mission through the year.

Running it out on a sunny day. While we tried to keep this layer on in the sun, we eventually took it off, until we hit the shade again. While it breathes well, the thicker construction just can't release heat as efficiently.

Photo: Amber King

Comfort and Fit

This base layer is comfortable with an attractive fit for our testers, and we believe it will work well for most wearers. It features 100% merino wool fabrics that feel luxuriously soft on the skin with flat seams. Next to skin, the materials are soft and plush, not even a little bit itchy. Unfortunately, it does stretch, and after wearing it for multiple days on end, this fabric doesn't bounce back until it's been washed and dried.

Long sleeves and plush cuffs equal excellent comfort features. One of the reasons we keep reaching for this top over others.

Photo: Amber King

We wore this top while climbing, hiking, and running through Colorado, Arizona, and Nevada. During our rigorous testing period, we wore it for four days straight (without washing!). The fit of this top is fitted with nice coverage throughout. The length is long through the torso and arms for ladies of any size. The collar is roomy as well. During these four days, the top never started to smell, even after 10-mile runs in the mountains. It did, however, start to stretch out a little bit after day two.

A look at the long fit of the arms and torso. This tester is 5"6, 145 lbs, with an athletic build wearing a size Medium.

Photo: Amber King

While this never changed the ultimate fit of the top and was hardly noticeable, it's a point of consideration. This was never an issue with the previous iteration that seemed to have a slightly thinner and lighter construction. That said, when throwing it into the washer and dryer, it came back to its shape and size. Overall, we love, love, love the comfort and coziness of this fabric. The trade-off is a little stretch when wearing it extensively for multiple days in a row.

The collar is stretchy with ample room. We also appreciate that we can tuck our chin when the going gets cold.

Photo: Amber King

Layering Ability

The slim construction offers decent layering ability. The ¼ zipper design will layer a tank top or shirt underneath, much easier than any crew top. It doesn't ride up, stays in place, and ultimately layers well in any outdoor outfit.

Layering over a tank top is pretty easy!

Photo: Amber King

To layer jackets or fleeces over top of this base layer, you need to do a bit of work, especially if your fleece is tight. This is because the face fabrics are fuzzy and have a little more friction than tops that integrate synthetics or polyester. Under a looser fleece or jacket, though, it does just fine. Add it to your winter collection and layer it as apart of your winter adventure wear with ease. Just know that you have to hold the cuffs of the shirt to prevent the arms from bunching up while layering. It doesn't ride up and stays in place while you move all day long.

The Smartwool Merino 250 our favorite top for wearing under a vest or jacket.

Photo: Amber King

Durability

So far, so good. The 100% merino wool construction doesn't have any seams or material defects after our testing period thus far.

The newest iteration is a little thicker, which we imagine might be more durable than the previous version (which feels a little thinner). That said, we owned the previous version and used it regularly for two years and didn't experience any issues. Since this top is very similar, made from the same company and materials, we expect the same performance in this regard. That said, given the merino wool construction, we would recommend avoiding using it for highly abrasive activities. In general, merino wool is a little less durable than synthetic constructions and need to be handle with care. However, this tried and tested piece is one that's surprisingly durable for its material construction.

We tested this while running through the woods with a running pack on, while backpacking, and thrashing through the woods. In all cases, the materials hold up!

Photo: Amber King

Value

If comfort and quality are your top priorities, you'll see the value in this base layer top. There's very few that match it across the metrics. That said, the price is steep for some unless you find a great deal online. A good tip is to look for last seasons' model (which also rocks) and find deals on past colors. There are some tops with similar performance at a lower price, but none that are 100% merino wool with the same longevity and overall level of awesome. So, if you can afford it, we'd argue that the value is high.

Conclusion

The Smartwool 250 ¼ Zip is a midweight 100% wool base layer with an exceptional level of comfort and performance. This top performer is a favorite and has been over the last few years we've tested it. This iteration is a little thicker than any other option in our testing fleet, making it an ideal option for colder weather. Wear it as apart of a cold-weather layered outfit or on its own in warm weather. A great fit with plenty of stretch and comfort to last you through the coldest days of winter.

While we're not a fan of the polluted Uncompahgre River, we are pretty stoked on this base layer top! It's a favorite that's proved itself time and time again over the years.

Photo: Amber King