Marmot Isotherm Hoody

Marmot Isotherm Hoody

Breathable Insulated Jacket
Marmot Isotherm Hoody
$225, 13 oz. (men’s medium)
Sizes: men’s S-XL, women’s XS-XL

A puffy jacket that’s breathable? That holy grail of backcountry apparel seemed elusive until Polartec Alpha synthetic insulation entered the scene. Looking for a fairly lightweight, Alpha-filled jacket that would be versatile for year-round use—and that has a hood—I used Marmot’s Isotherm Hoody on spring and summer hiking trips. Although just 13 oz., this full-zip jacket kept me warm on mornings ranging from calm and 15° F. (with a warm top on underneath it) in southern Utah in late March, to the 40s with steady winds of 40 to 50 mph in Idaho’s White Cloud Mountains in July. Even more impressively, on a frosty morning in the teens and 20s in Utah’s Grand Staircase-Escalante National Monument, I could wear it hiking at a brisk pace without overheating.

How is a puffy jacket breathable? Alpha’s durable, stable characteristics allow manufacturers to put it in garments with a woven shell fabric made with a more open construction, making the shell more air permeable—i.e., more breathable. So unlike with traditional puffy jackets, whether down or synthetic, you can be active while wearing this piece. The Isotherm Hoody combines abrasion-resistant Pertex Quantum fabric with a highly breathable mesh lining for insulation that hits the trifecta: warm, breathable, and tough. Shoulders are reinforced with soft-shell fabric for enhanced breathability and durability under pack straps. Like other synthetic insulations, Alpha retains its ability to trap heat even when wet, and dries reasonably quickly.

The Isotherm Hoody packs down to slightly larger than a liter bottle. The fit allows for layering a light fleece underneath, and is trim enough to pull a shell jacket over it. Freedom of movement is excellent for arm-swinging activities like climbing or using poles going uphill. The elasticized cuffs and hem kept out drafts, and the adjustable hood moved with my head when I looked to either side. There are two roomy hand pockets and a chest pocket, all zippered.

So what’s it good for? As someone who normally gets quite warm when active, I found the Isotherm Hoody comfortable when hiking in temps well below freezing; once the air warmed up to freezing or above, the Isotherm was too warm for me to wear while on the go. But people who get cold easily will really benefit from insulation that breathes while delivering a good amount of warmth for its weight and bulk. This jacket serves multiple functions, from a pure insulation piece in camp on three-season backpacking trips to an on-the-go fall, winter, and spring garment when hiking, snowshoeing, backcountry skiing, or climbing.

The hoodless Isotherm Jacket is $200 and 12 ounces (men’s medium).

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See all of my reviews of down and puffy jackets and all of my reviews of outdoor apparel, as well as my article, “The Simple Equation of Ultralight Backpacking: Less Weight = More Fun.”

NOTE: I’ve been testing gear for Backpacker Magazine for 20 years. At The Big Outside, I review only what I consider the best outdoor gear and apparel. See all of my reviews by clicking on the Gear Reviews category at left or in the main menu.

—Michael Lanza

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