Best warmth-to-weight from a mainstream outdoor brand.

We value warmth-to-weight above all else in an ultralight sleeping bag, which is why we like the Therm-a-rest Hyperion 20. Based on our modeling, it has the highest warmth-to-weight ratio of any conventional 20F ultralight sleeping bag from a mainstream outdoor gear brand. It’s only bested by designs from ultralight cottage industry brands like Zpacks. Shop now.

• Weight: 20.0 oz
• Price: $550
• Down: 900 fill power hydrophobic goose down
• Fill Weight: 12.5 oz
• Fabric: 10D Nylon Ripstop
• ISO tested comfort: +32 F
• Pros: Ultralight. High warmth-to-weight.
• Cons: Expensive. Narrow. Slightly under-filled.

Features

This is achieved through the use of 900 fill power down, in conjunction with a relatively lightweight 10D shell fabric, and a snug fit. Additionally Therm-a-rest also states that they have intelligently distributed the down. In this ultralight sleeping bag, 70% of the plumes are in the top section where it works harder to insulate rising heat.

Prioritizing the top insulation and de-prioritizing the back is quilt-like in its design mentality, and we think it’s a cool and innovative choice. We believe that is at least part of what allows Thermarest Hyperion 20F to be lighter than almost all similarly comfort temp rated bags.

As you can see in the photo, Hyperion has a pretty slim design, and an exceptionally small footbox. While decreasing interior volume decreases comfort, it increases warmth. Heat radiating off one’s body is condensed throughout a smaller total space, rather being distributed and diluted.

In this case, our modeling agrees with ISO that this bag is comfortable down to 32 degrees and think it will handle most 3-season backpacking conditions with aplomb. However, if you run cold, you consider a bag with a slightly lower comfort rating.

Verdict

The Them-a-Rest Hyperion 20F is a narrow mummy, but otherwise an incredible backpacking sleeping bag, and will serve ultralight backpackers very well.

Read about more great options in our guide to the best backpacking sleeping bags, or crank up performance to the next level with our guide to the best backpacking camp quilts.