My favorite pieces of gear are the ones I just wasn’t on board with in the beginning: maybe I don’t understand the function it, maybe I don’t buy into the gimmick (the Airvantage jacket anyone?), or maybe I’m just feeling vain and don’t like the look of a thing.
This was exactly the case when I got my hands on a Marmot Isotherm Half-Zip. In my eyes, it had the aesthetics of my grandfathers windbreaker, and had a claim that (at the time) was relatively new to a lot of us: breathable insulation.
I was skeptical. And (spoiler) I was wrong.
Polartec Alpha, as many of us now know, is a “breathable insulation,” meaning its not designed to be your main, sitting-on-belay puffy, but rather is meant to be put on and left on all day. This is just an extension of a notable trend in outdoor gear of late which is to look for
moisture management and breathability as key components to a piece being your backcountry best-friend versus a closest-stuffer. Temperature and moisture regulation, not full-on control, is the name of the game.
Its a fine idea, but does it really work? I was hesitant, but as someone who was constantly shedding layer on my High Peaks hikes I figured “what the hell.”
FEATURES (or, a healthy lack-there-of)
I went with the Half-Zip over its more burly, and more insulated Full-Zip and Hooded brothers, believing (correctly) that it weighed a lot less and that I likely wouldn’t need that much insulation. Now, the confusing thing was I couldn’t actually tell if the different pieces had different amounts of insulation, but the weight savings between the other jackets and the half-zip was a full 8 oz’s. Unlike Primaloft, which often comes with how many grams of insulation the piece has, I was left to estimate, but I believe my assertion is correct.
Unlike its brothers, the Half-Zip is significantly paired down. No cool soft-shell shoulders, no hood (which I honestly never use): a light Pertex shell, a thin amount of Polartec Alpha insulation, a mesh liner (not like your dad’s old windbreaker-mesh–it’s a tighter knit), napoleon zipper (packs into itself), drawcord hem, and a partial elastic cuff. That’s it.
And that’s all it needs. I chose the no-hood option because it was undoubtedly going to get layered under or over other things, and the last thing I needed was another errant hood flapping in the breeze or curling up against my neck, whispering “Why have you forsaken me again, father?”
The jacket is impressively compressible. It fits nicely into its own pocket without having to cram it in and stress the seams, and has a gear loop to attach it to a harness (great for ice climbing…if you even have to take it off). The half-cuff elastic is absolutely awesome too: I’ve been able to slide it on and off over my thinner ice-climbing and liner gloves without it catching and getting stuck, so that’s a great design. Marmot often excels at little details like this.
First, the fit (always the most important). At 6’1″ and 155 lbs, I represent the gangly end of the spectrum. I had expected them to go with an athletic cut instead of the standard fit it actually is, but this was a good choice on their end, as I am able to layer multiple baselayers underneath. But, Marmot recognizes the piece is going to go under things, and thus it also is trim enough to fit under your other layers.
Compared to the famed Patagonia NanoAir, I like the cut better: the NanoAir’s a nice piece, but I can (in a comparable sized Medium) literally wear another primaloft jacket underneath it, meaning it bunches when the piece itself is under a shell. Not so with the Isotherm: I still had a little more room, but I believe this accounts for my thinness. If you’re a regular human, this should fit fine in your normal Marmot size. They really dialed in the fit for the piece’s intended function, and I like that.
…over fashion, I told myself as I pulled it out of my pack the first day, standing at the junction of Wright and Algonquin in the ADK High Peaks. This jacket looks like so many unassuming, old anoraks that I see come into our shop used. It seems silly, but in age when jackets come with cool contrast zips, geometric baffles, and zonal constructions that make your average hiker look like he’s from TRON (in a good way–I love it), this piece was so unassuming. But what the hell, I wanted to try it.
My test was simple and rigorous–not scientifically, but for me. I first put on a thin fleece (think R1 weight) and power-hiked up to Wright, then descended; for the similar hike up to the peak of Algonquin, I would wear the Isotherm.
My trip up Wright went as it normally did, hard hiking with a few breathers to cool down, and at the peak I popped on a thin down puffy and a shell to keep the wind off my damp back as I took in the view for a while. Then I stripped back down and scrambled down to the junction before changing and ascending again.
Algonquin was a hard hike up, and at the top I stopped to chat with some new trail friends I’d made, grab some food and water, and talk with the Peak Steward, and this all happened so unassumingly that I realized I never adjusted my layers. In fact, I was bone dry, even my back that had been sweated out before. There I stood on the summit, wearing only the wind-blocking, heat-regulating Isotherm. I’m sure I got warmer on the hike up, maybe had to unzip a little, but I never had to think about it.
That’s the amazing thing, I now realize, about these breathable insulations: you really can leave them on all day without thinking about it. Of course, there are times when its too warm, or you need to bust out the big-downy-guns, but for the most part things will layer above the Isotherm, but it will always stay on. It’s almost like a base layer in that regard.
The next year with the Isotherm was a good one: lots of cross-country skiing, backpacking, hiking, kayaking (love it for this–I often get motion-sick and overheated, and this prevents it), and rock and ice climbing, and for almost every trip the Isotherm made an appearance. It’s infinitesimal in the pack, but seldom does it ever go into it. I don’t run in it (some folks might–I just get hot if I wear anything more than a baselayer and softshell), but anytime I’m hiking hard enough to get out of breath, or I’m climbing a dripping waterfall, or am even just going for a leisurely fall hike, the Isotherm is my constant companion…just not once I get back to town.
Is the Isotherm essential to your kit? No. Pieces like this are for folks who are out enough to really lose a noticeable portion of their life to changing layers every five minutes. The Isotherm will never break a trip because you didn’t have one, but having one will make every trip a little drier and a little more comfortable.
Written by Chris, who once broke a tree with his face.