Icebreaker Merino 200 Sonebula Base Layers Review

The Icebreaker Sonebula thermal base layer set is a midweight, 100% merino wool next-to-skin layer for hikers and backpackers. How do these thermals hold up to the rigors of the trail? Are they better as camp clothes or active layers? Keep reading to find out.

icebreaker merino 200 sonebula thermal top

This guy wears it better than the reviewer, trust me. Enjoy. Courtesy

Icebreaker Sonebula Base Layers At-a-Glance

Merino 200 (gram) Sonebula Thermal Leggings

  • MSRP: $110
  • Weight: 6.3 ounces
  • Material: 100% soft merino fibers

Merino 200 (gram) Sonebula Long Sleeve High Neck Thermal Top

  • MSRP: $110
  • Weight: 8.6 ounces
  • Material: 100% soft merino fibers

Circumstance of Review

I’ve tested both leggings and top throughout the autumn and winter in a relatively mild climate in the southeastern United States. I used them camping in lows down to 40 degrees and wore them as night clothes indoors on numerous occasions. I also ran several times in the top, including in heavy rain and temperatures down to the mid-30s with winds of 20 mph.

Icebreaker Sonebula Long-sleeve Top and Leggings Review


  • 100% soft merino wool Natural, annually renewable fiber that resists odors, insulates when wet, and regulates body temperature in a variety of conditions.
  • Soft Geometry Seamlines – Allow for maximum mobility and comfort.
  • Raglan sleeve construction (top) — Allows for maximum mobility.
  • Flatlock seams — Helps prevent friction.
  • Drop-tail hem (top) – Provides added coverage
  • Gusset — Provides for mobility and comfort.


These warm base layers are designed with colder weather use in mind, whether for skiing or backpacking. I didn’t use the pieces in extremely cold weather, but they kept me very warm indeed. I did find the top too hot during 6- to 10-mile runs as well as hiking in 30- to 40-degree temperatures. I purposely allowed the top to get wet on a number of occasions and found that it insulates very well even wet. They are warm and comfortable as camp clothes (mostly; see below) though much too warm for my tastes beneath a 20-degree quilt.

icebreaker merino 200 sonebula thermal leggings

And here’s another view of the model guy, with just the slightest li’l stomach pooch. Again, enjoy. Courtesy


I found the top generally comfortable, though if I’m honest, I probably should have gone with a medium instead of a small (which usually works and seemed to be the right size based on Icebreaker’s sizing information).

I went back and forth about the two-inch collar. I love wearing mock-turtle shirts, but for some reason (again, possibly a sizing issue) the collar at times felt more restrictive than I prefer.

The merino fibers are as soft as advertised, and mostly quite comfortable. That said, for me, there always comes a point when I recognize the slightest itch here and there, at least in comparison to a technical-fiber piece (or cotton; but we all know it’s generally a no-no for hiking).

icebreaker merino 200 sonebula top

Racing stripes. What other base layer offers racing stripes? Photo by Jody Frank Evans.

I really appreciate the seam construction and underarm gussets, which reduced rubbing and the potential for chafe to zero for me.

As mentioned above, merino really does insulate even when wet, and that is extremely important to me. The material was clingy after a soaking in a hard downpour, but what wouldn’t be? It dried quickly, considering I live in a humid climate.

I found the top too warm for the kind of conditions I usually run in, but I can well imagine it would be just about right for skiing on a cold day.

Weightwise, 8.6 ounces is a significant hit to my base weight. While hiking the Pacific Crest Trail in 2021, I ended up shipping my REI merino base-layer shirt home, mostly to lose a whopping 11 ounces of pack weight; the Icebreaker piece is an improvement on that, but still perhaps a little heavy for long-distance hikers concerned about weight.


I didn’t give the leggings as much of a workout as the top, simply because I can tolerate bare legs in temperatures well below 30 degrees. However, I made a point of wearing them in camp and while sleeping.

For wearing around camp, when I do tend to get cold, the leggings were excellent. Comfortable and soft, with just the slightest hint of itch once I got warm.

Icebreaker’s Merino 200 Sonebula leggings are a great option for camp wear. Photo by Jody Frank Evans.

I appreciate the common-sense decision to eliminate the always-useless (IMO), complicated front flap you find on so many base layer bottoms and underwear. Seems to me they add weight and bulk (even if only a little) for no reason, since I (and most other guys?) usually don’t bother trying to work ol’ Willy through the maze and just tug the waistband down when nature calls.

Again, my legs tolerate cold extremely well. But I’m sorry I didn’t take the opportunity to run in the leggings during one wild, windy, wet, cold morning in January, because I’d like to know if they made a difference. I’m guessing they would have.

I love the cool “racing stripe” on both top and leggings (kale/spice — translation: gray-green/orange—colorway in my testers),  though it appears that the colorway options are down to one (midnight blue/white).

Icebreaker Merino 200 Sonebula Base Layer Pros

  • Very warm
  • Soft, comfortable material
  • Good insulation when wet
  • Quick-drying
  • Seam construction and gussets aid mobility and reduce chafe
  • Fun two-color design
  • Price reasonable within market norms
icebreaker merino 200 sonebula base layer

Icebreaker’s Merino 200 Sonebula base layers are pretty warm, best suited for significantly cold weather. Photo by Jody Frank Evans.

Icebreaker Merino 200 Sonebula Base Layer Cons

  • Very slight itch on occasion
  • Potentially confining for long use
  • A little heavy for most three-season backpacking
  • Feel more suitable as camp clothes than active-wear except in very cold conditions


I really like this Icebreaker set and found it especially warm and comfy during the coldest parts of winter (tangent: Does anybody else feel like their house is always cold when it’s like 65 degrees outside?). The faint woolly itch is more than tolerable and, had I requested medium rather than small, I suspect my occasional issues with feeling confined would disappear.

All that said, these really do feel more like camp clothes to me than hiking clothes. They’d certainly be nice to have when, say, you’re caught in a blizzard on the Continental Divide, but the weight and (excellent) insulating capacity may outweigh the benefits on a long hike.

Shop Icebreaker Sonebula Base Layer Bottoms

Shop Icebreaker Sonebula Base Layer Shirt

Comparable Base Layers

Smartwool Intraknit Merino Base Layer Crew Top and Leggings

MSRP: $120 each
Weight: 7.34 ounces (men’s medium top); 9.38 ounces (men’s medium leggings)
Fabric: 53% merino , 45% Polyester, 2% Elastane

REI Co-op Merino 185 Long-Sleeve Base Layer Top and Leggings

MSRP: $79.95 (each)
Weight: “Lightweight” (manufacturer does not provide actual weight)
Fabric: 100% merino wool

Arc’teryx Motus AR Top and Leggings

MSRP: $79 (each)
Weight: 5.1 ounces (leggings); 5.5 ounces (top)
Fabric: Engineered polyester

These Icebreaker Sonebula base layers were donated for purpose of review.

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