Smartwool Merino Sport Ultra Light Review

Our Analysis and Test Results

Skillfully employing Merino 150-weight mesh into large underarm vents, the Merino Sport UL is a perfect jacket for runners to take from the starting line to a night on the town. Despite its ultralight nylon construction, this jacket provides solid wind and water resistance — we found ourselves impressed on both a blustery ridgeline and a light rain after a long adventure run.

Performance Comparison

This jacket was one of our favorites for trail running, thanks to awesome ventilation and comfortable mobility.

Photo: Jill Rice

Wind Resistance

For a shell designed as a breathable outerlayer, the Merino Sport UL is impressively wind resistant. The thin nylon build is ultra-lightweight, so don't expect it to be warm on its own, especially in a strong, wintry wind. But our lab testing supported what we found in the field, that this jacket does a nice job of keeping gusts from penetrating to the core — just as long as you don't have your arms in the air.

Better facing the wind than catching it to the side... the large underarm vents were definitely an entry point for a cold wind to chill us to the core.

Photo: Jill Rice

A small, elastic cinch point — combined with Merino mesh panels on the inside — work together to keep the hood in place, and your ears warm when the wind really picks up. We do wish that designers included a drawcord at the hem, as air can easily stream from the bottom up and out of the underarm vents and can cause the jacket to billow. But the inclusion of a storm flap behind the zipper will help keep you protected from head-on winds.

Breathability and Venting

A top performer in terms of breathability, the highlight of the Merino Sport UL are the two huge underarm vents. These body-mapped panels are made out of Merino Sport mesh, and true to Merino-form, do a fantastic job of wicking away moisture from the sweatiest part of our body. These mesh panels work in conjunction with smaller vents across the top of the shoulders to keep a consistent flow of air across an area that tends to trap heat.

Body-mapped, Merino wool vents... how better to improve efficiency of breathability?

Photo: Jill Rice

After a particularly tough run, we did observe that there was a sweat-soaked pattern across the upper back. But without noticing any heat pooling in these areas during our run, it certainly didn't affect the comfortability of movement over miles of trail.

Smaller, slot-style vents on the shoulder help improve airflow throughout the jacket.

Photo: Jill Rice

Weight and Packability

This jacket claims "ultra light" status in its name, and while not all marketing claims are true, in this case we have to agree. The Merino Sport UL tips the scales at sub-five ounces, and even more importantly, feels equally light and airy to wear.

Smaller than a standard Nalgene bottle, this packed-parcel was easily further compressed to nearly half this size.

Photo: Jill Rice

A fully squared-off pocket makes it much easier to stuff into itself than others. The storage pocket includes a harness loop and a small, corner drain hole — to afford a bit of airflow to help fight off any mustiness, just in case you end up packing this jacket away before it fully dries out.

Simple weather protection in an ultralight package.

Photo: Jill Rice

Fit and Functionality

The Merino Sport UL, while indeed sporty, has one of the nicer cuts out of our current crop of wind jackets. The athletic fit airs on the tighter side, but offers a looser hem that lies flat and doesn't bunch up when on the move. If you're looking to fit in with the 26.2 crowd then this jacket has the simple, runner's style that works well out on the town, whether you're clocking miles or hanging out with friends.

Light enough to float, warm and breathable enough to keep things moving even in snowy weather.

Photo: Jill Rice

The inclusion of body-mapped panels is a thoughtful addition, not only in terms of breathability but also with regard to mobility. The Merino mesh panels offer just the right amount of stretch, and the Merino lining of the hood is soft next to your face, both worn down and when you have to go hood-up. While the elastic at the back of the hood does a good job of keeping it in place — particularly when wearing a hat — we do dock this jacket some points for not having a drawcord at the hem to help cinch down when the wind really picks up.

Smartwool keeps the weight of this jacket down by cutting out drawcords, instead opting for a single elastic band at the back of the hood to hold it in place.

Photo: Jill Rice

Water Resistance

The DWR finish on the Merino Sport UL was one of the most effective in this review. In our shower-test, the water-repellent coating was awesome at beading up water and allowing it to smoothly run-off the jacket front. We were a bit worried about the size of the underarm vents as an access point for weather, but the natural-hydrophobia of Merino wool seems to help keep any light rain at bay.

Good for a long-while, but under the weight of continuous snowfall we found that this nylon shell soaks through in patches, particularly in the arms and shoulders.

Photo: Jill Rice

The Merino Sport UL is prepared for quick-passing storms. But we found that under more consistent precipitation — like a light snowfall over the course of a ski tour — that the thin nylon of the jacket is more prone to soaking through over a period of hours.

A quality DWR finish does quick work of beading up rain water, as verified in our lab testing.

Photo: Jill Rice

Value

As with any product involving the revered material that is Merino wool, the Merino Sport UL carries a slightly higher price tag than many of the other jackets included in this review. However, we believe that this wind jacket does offer a solid value based on its performance — particularly if you are a runner, or engaged in high-intensity activity where breathability is paramount.

A perfect addition to the runner's closet, keeping you comfortable when on the move all year-round.

Photo: Jill Rice

Conclusion