Therm-a-Rest Hyperion 20°F

Warmth: 4.8

You might forget you have the
ultralight Hyperion in your pack, but you’ll definitely notice its warmth come nighttime. We spent a 23°F night on the shores of Grand Teton National Park’s Leigh Lake and were thrilled to wake up warm despite the snow on the ground. On another night in Grand Teton, a rainstorm brought humidity to nearly 100 percent as we hunkered down, but the Hyperion’s hydrophobic, 900-fill down didn’t get wet and remained lofty.

Comfort: 3.9

One sacrifice the Hyperion makes in order to be ultralight and ultrapackable is in its shape. With shoulder and hip girths of 57 and 49.5 inches, respectively, it’s narrower than most bags we tested—there’s not much elbow room, which may be an issue for those with broad frames or who like to side- or stomach-sleep.

Features: 3.8

A half-zip helps save weight, but isn’t great for ventilating on warmer nights and is a bit snag-prone. The Hyperion comes with easy-to-use straps that loop around a sleeping pad, minimizing how much we slid around when were sleeping on uneven ground. Although the 10-denier ripstop shell is thinner and less durable than other bags tested, we appreciated the wispy fabric’s ultralight tradeoffs.

Packability: 4.9

Not only a stand-out as the lightest bag in our test, the Hyperion is also the smallest when compressed: It squishes down to just a little bigger than a 1-liter Nalgene.

Overall: 4.4

$410; 1 lb. 4 oz.; 20°F; small, regular, long