Gear Review: Marmot Ion 20 Sleeping Bag

Marmot Ion 20 sleeping bag.
Marmot Ion 20 sleeping bag.

Sleeping Bag
Marmot Ion 20
$419, 1 lb. 13 oz. (regular)
Sizes: regular and long ($439)

Heading into Washington’s North Cascades National Park for an 80-mile backpacking trip in the last week of September, I didn’t want to take a chance on gear and clothing that might not stand up to cold, wet weather, maybe even sub-freezing nights and snow in that notoriously soggy mountain range. The hybrid-insulation Ion 20 fit the specs for that mission, thanks to its blend of high-quality down feathers and synthetic insulation and super warmth for such a lightweight bag.

I slept in it for four nights in the North Cascades, in mostly dry weather with lows that actually didn’t drop below around 40° F, and for one mid-October night in the 40s in Great Smoky Mountains National Park, when I slept outside, under the stars, without concern about dew settling on the bag. It was more than warm enough for those temps for someone who, like me, sleeps warm. I left it partly open every night, discovering the utility of Marmot’s nine-inch-long, “fold-down” second zipper, which lets you open both sides of the bag at your chest and shoulders for added ventilation, but also makes it easier to sit in the bag in a tent or in camp and keep both arms outside to use your hands for tasks. I think the Ion 20 is true to its EN comfort temp rating of 28° F (the EN lower limit rating is 17° F and the extreme rating is -15° F), but also that people who sleep cold would find its warmth perfect for three-season camping.

Marmot Ion 20 hood.
Marmot Ion 20 hood.

Marmot’s Composite Construction achieves the benefits of down (high warmth-to-weight ratio) and synthetic insulation (retains warmth when wet) by combining 850+-fill goose down around the body, head, and feet, with synthetic Thermal R Micro insulation on the bottom of the bag. Sporting nearly five inches of loft, the Ion 20 looks warm. The hood’s intricate, multi-baffle design delivers a close and comfortable fit when sealed up tight, while the wrap-around construction at the feet increases warmth at the typically coldest end of a bag. The curved-baffle construction minimizes unwanted migration of down feathers.

Marmot Ion 20 foot box.
Marmot Ion 20 foot box.

With a 60-inch circumference at the shoulders, 58 inches at the hips, and 41 inches at the feet (in the regular bag), I’d rank the roominess of the Ion in the middle of the pack of mummy bags: There’s enough space to not feel confining, and I could get dressed and undressed inside it; but sleeping on my side, I had to fold my arms up pretty close to my torso. The nearly full-length main zipper’s slider never snagged. The Pertex Quantum shell fabric is strong for its low weight, allowing maximum insulation loft while not leaking feathers or being susceptible to zipper snags. The combination of 12-denier and 15-denier nylon mini ripstop fabrics in the shell and lining also helps prevent zipper snags, but demands a little caution in handling the bag outside to avoid tears. The Ion 20 stuff sack measures 16×7 inches, but I packed the bag into a slightly smaller, roll-top stuff sack, so it didn’t fill the bottom of a 55-liter backpack.

The Marmot Ion 20 delivers equally high value and performance: You won’t find many bags with this temperature rating that are under two pounds, or with this level of quality of materials and construction at this price. It’s a good choice for anyone who routinely heads out in cold, wet mountains, or someone who wants extra warmth in a three-season bag without extra weight or bulk.

BUY IT NOW You can support my work on this blog by clicking this link to purchase a Marmot Ion 20 at

See all of my reviews of sleeping bags that I like and all of my reviews of backpacking gear, and my articles “Pro Tips: How to Choose a Sleeping Bag” and “10 Pro Tips: Staying Warm in a Sleeping Bag.”

See also my stories:
The Simple Equation of Ultralight Backpacking: Less Weight = More Fun
Buying Gear? Read This First
Ask Me: How Do We Begin Lightening Up Our Backpacking Gear?
10 Tricks For Making Hiking and Backpacking Easier
My Top 10 Favorite Backpacking Trips

NOTE: I tested gear for Backpacker Magazine for 20 years. At The Big Outside, I review only what I consider the best outdoor gear and apparel. See categorized menus of all of my gear reviews at The Big Outside.

—Michael Lanza

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2 thoughts on “Gear Review: Marmot Ion 20 Sleeping Bag”

  1. Hi Nancy, I think a draft collar often makes a difference, but that also depends on the design of the hood. The Ion 20 has a hood that closed up snugly for me. Note that the EN comfort rating is 28 degrees F, and many summer bags rated about the same often lack a draft collar.

  2. Could you comment on the top of the bag, which doesn’t have a dedicated draft collar. Does its design seem to snug-up just as well?