Review: Big Agnes Storm King 0 Sleeping Bag

Winter Sleeping Bag
Big Agnes Storm King 0
$380, 3 lbs. 9 oz. (regular)
Sizes: regular and long ($400)

When is a mummy-style bag too constricting? I’ve used ultralight, three-season bags that felt a little too coffin-like. But in winter—or wintry conditions, such as you encounter when mountaineering in spring and summer—there are more practical reasons to use a bag with extra space, and you get it with the Storm King 0. Beyond its dimensions, the Storm King’s water-resistant down feathers, fairly unique “system” design that requires sliding an air mattress into a sleeve on the bag’s bottom side, and its relatively affordable price for this category of bags merits a close look.

My son, Nate, approaching our high camp climbing Mount Whitney.
My son, Nate, approaching our high camp climbing Mount Whitney.

My 15-year-old son and I swapped off using this bag and another 0-degree model for three nights camping on snow in temperatures as low as the teens Fahrenheit on a four-day climb of the Mountaineers Route on California’s 14,505-foot Mount Whitney in mid-April; and for three mid-February nights skiing and snow camping in Idaho’s Boise Mountains, with lows ranging from just below freezing to the mid-30s. While I found it too warm for temps above freezing, my 13-year-old daughter, who gets cold very easily, loved this bag’s warmth on a backpacking and car camping trip in March in southeastern Utah, with lows from the 40s to below freezing.

The semi-rectangular Storm King is noticeably roomier than many backcountry bags: the regular measures 70x65x53 inches. I could easily roll around, get dressed inside the bag (a big plus in sub-freezing temps), and sleep in more natural and comfortable positions—closer to the experience of sleeping in my own bed (except for the snow). I stuffed my pants and base layer top deep into the vaulted foot box (which has more space for feet than most backcountry bags), both to add a little insulation for my tootsies and so my clothes would be warm in the morning. And yet the bag’s space doesn’t compromise warmth by having too much real estate for a small person to heat up: My son and daughter, both slightly more than five feet tall and 100 pounds on these trips, stayed warm on nights well below freezing.

Big Agnes Storm King 0 sleeping bag.
Big Agnes Storm King 0 sleeping bag.

Inside the bag is 24.5 ounces (26.5 ounces in the long bag) of water-repellant, 650-fill Downtek down feathers, which resist absorbing water much better than standard down and dry faster once wet. While the 650-fill quality makes this bag a little bulkier and heavier than bags with higher fill power down, it’s also considerably less expensive—about three-quarters to half the price of many high-quality 0-degree bags—and the regular bag still compresses to a manageable 8×9 inches.

Like many Big Agnes bags, the Storm King lacks insulation on the bottom; it’s all on top, where it’s most functional (rather than getting flattened underneath you), and a mattress slides into a sleeve on the bag’s bottom to insulate you from the snow or frozen ground. As a side sleeper, I haven’t always liked this system because the hood doesn’t tend to turn with your head. But the Storm King’s redesigned hood now moves free of the pad sleeve: While it doesn’t turn a full 90 degrees with my head, it’s an improvement over the previous design, and the bag’s draft collar covers whichever ear is facing up. Plus, there’s an even stronger argument for this system—integrating the pad with the bag—in winter, when your bag sliding off your pad will make you cold fast and could wake you repeatedly.

Big Agnes Storm King 0 sleeping bag hood.
Big Agnes Storm King 0 sleeping bag hood.

The fat hood, collar, and draft tube along the non-snagging zipper keep warm air in and cold air out. The shell fabric isn’t waterproof, but is treated to repel moisture, which protects against moderate condensation inside a tent. Stretch fabric on the sides of the pad sleeve accommodates air mats in a range of thicknesses. Lastly, I like the stretch-fabric pillow pocket beneath the hood.

Whether you’re camping in winter conditions, just prefer a more spacious bag, or like the Big Agnes system of incorporating the air mattress into the bag, the Storm King 0 sleeping bag offers several reasons to recommend it.

BUY IT NOW You can support my work on this blog by clicking this link to purchase a Big Agnes Storm King 0 sleeping bag at

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

See also my stories:

12 Pro Tips For Staying Warm Outdoors in Winter
Review: Gear For Climbing Mount Whitney
Ask Me: How Can You Tell How Warm a Down Jacket Is?
The Simple Equation of Ultralight Backpacking: Less Weight = More Fun

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 my Gear Reviews page at The Big Outside for categorized menus of all of my reviews and my expert buying tips.

—Michael Lanza


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