A scene from the movie Blackhawk Down has one soldier taking the heavy back panel out of another’s flack vest—he wouldn’t need it, the theory went, because he wouldn’t be running away from the enemy. Marmot’s Fusion jacket actually makes me think of this with its Pertex® Woven fabric protecting the front from the elements. The back has to make due with stretch nylon, so as long as you’re attacking, you should be good.

Whatever forward-motion activity you like, from trail running to alpine hiking to climbing and bouldering, the highly breathable attack-mode Fusion is up for the task. This is a four-season ultra-marathon runner’s fleece, a light insulator for an alpine climber who doesn’t let the weather’s swing end the hike. It’s a no-compromise athlete’s version of the comfort the rest of us would seek by running on a treadmill in a gym instead of into the teeth of the wind or rain.

I respect the Fusion for what it is—a lightly insulated layer for when a rain shell isn’t quite appropriate but a fleece or heavier insulator is too much. The Fusion’s best times are when I’m in attack mode; slow down on those cool mornings and you might want more warmth. You don’t slow down in this jacket, you attack-attack-attack! Take no prisoners!

Some niggles: no interior pocket for my tunes, which the Atomic provides. But the Atomic is actually more the runner’s light insulator of choice, and the Fusion slots more for that alpine hiker/trail runner/climber sort who need the back and arms’ flexibility. The pockets are a little low for the waist belt of some packs, so this might be slightly more comfortable as an afternoon jacket for unencumbered outings.

The thumb holes keep the sleeves in place no matter how you reach, stretch, or move. It actually reminded me a little of a very stretchable, breathable option for a mid-layer in colder weather, under a great shell when the weather is really bad and standing alone when it breaks up.

The Fusion probably finds its niche in areas like the Cascades where it can be cool and damp, and I think that it might do well for cool days for a sport climber. Whatever the activity, as long as you’re in attack mode, the Fusion is a good option to have on your side. Check it out on Marmot’s website where at $145 it lands around the middle of the pack in price. But whatever you do, don’t turn your back on it—attack!