My partner and I each brought two sleeping pads to make base camp on Alaska’s Tokositna Glacier a bit more luxurious this past May. By the end of two weeks, though, I was using just one, while my partner had three. Cold still seeped through his synthetic bag, while I slumbered toastily in my Sonic -20 from Nemo.
My favorite thing was the foot box, which has an extra layer of synthetic insulation—in addition to the 800-fill hydrophobic down layer used in traditional baffles in the rest of the bag. Even when my feet were mashed against the side of the tent or hanging off the end of the pad, they stayed warm. The body of the bag widens slightly at the knees, while retaining a classic mummy shape.
On those super-cold mornings, we would wake up to the drip-drip-drip of melting frost (read: frozen sleep breath) plastered to the inside of our tent. The Sonic’s -20D ripstop nylon (40D on the foot box) repelled water well—the droplets simply beaded down the side and the insulation stayed lofty—and never snagged despite all the sharp objects we forgot to leave outside the tent.
The Sonic’s flagship features are two lengthwise vents, dubbed “thermo gills,” which act to separate the adjacent lengthwise baffles slightly. They allow you to moderate the temperature without actually unzipping the bag itself, and they certainly work to an extent. Then again, I was rarely too warm, so mostly kept ’em zipped up.
My one frustration was the Velcro closure on the bag’s draft collar—a baffle that wraps around the inside at neck level to keep the warm air from escaping. Even the slightest movement was enough to undo the Velcro, decreasing the draft collar’s effectiveness in keeping cold air out.
Given its price of $569.95, you’ll be hard-pressed to find a cheaper bag of similar rating, and at 3 pounds 8 ounces, it’s about as light as you’ll find for a -20-degree bag. In its stuff sack, the Sonic fits inside your average microwave with plenty of extra space. While this isn’t the bag for super light-and-fast climbs with open bivies, if you’re in a tent in the big mountains—base camp or en route—the Sonic is a solid choice.
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