Therm-a-Rest Hyperion 20°F Sleeping Bag
The Hyperion 20°F is our lightest bag built for serious backcountry use. At just 1 lb 2 oz in the regular length, it pairs 900-fill Nikwax Hydrophobic Down with a minimalist mummy taper to deliver warmth where you need it without carrying unnecessary weight.
We designed this bag for alpinists and fastpackers who count every ounce. The 10-denier shell fabric shaves grams while the box-baffle construction keeps loft even across cold nights. A full-length zipper gives you ventilation control, and the SynergyLink™ Connectors integrate seamlessly with our sleeping pads to eliminate cold spots beneath you.
Specifications & construction
Hydrophobic down & box-baffle insulation
We treat every ounce of 900-fill down in the Hyperion 20 with Nikwax Hydrophobic technology. This water-repellent coating keeps the down from clumping when exposed to condensation or light moisture inside your tent, maintaining loft even on multi-day trips through variable weather.
The box-baffle construction creates individual chambers that prevent down migration. Cold spots form when insulation shifts overnight—our baffles lock each fill cluster in place so you wake up as warm as you fell asleep. The 10-denier ripstop shell minimizes weight while the liner wicks moisture away from your skin.
Mummy taper & weight distribution
The Hyperion 20 uses a tapered mummy cut that follows your body’s natural shape. We trim excess fabric at the feet and shoulders to eliminate dead air space that your body has to heat, then add insulation volume around your core and along the zipper draft tube where heat loss is highest.
Regular length measures 6 feet with a 1 lb 2 oz pack weight. Long length extends to 6 feet 6 inches and adds 3 ounces. Both sizes compress to a 6 x 8 inch stuff sack that fits easily in the bottom of a 40-liter pack. The same ultralight philosophy we apply across our sleeping bag collection drives every design choice here—strip away what you don’t need, reinforce what you do.
SynergyLink Connectors & pad integration
Eliminating the cold gap
Most sleeping bags slide off your pad during the night, creating a gap where cold air steals your warmth. Our SynergyLink Connectors snap directly to compatible Therm-a-Rest pads, locking the bag in place so insulation stays between you and the ground.
How the system works
Two webbing loops on the bag’s underside click into the pad’s ToeHook feature. This creates a unified sleep system—the bag can’t twist or bunch, and you don’t wake up lying on bare nylon. The connection also means you can carry less insulation on the bag’s underside since your pad handles the compression zone, shaving additional ounces without sacrificing warmth.
Lightweight sleeping bags for three-season backpacking
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Questions about the Hyperion 20°F
The Hyperion 32 uses the same shell fabric and construction but contains less down insulation, making it lighter and more packable for summer trips. The 32-degree bag weighs 15 ounces in regular length compared to 1 lb 2 oz for the 20-degree version. Choose the Hyperion 20 for spring and fall shoulder seasons or high-altitude summer use. The 32 works best for warm-weather backpacking below 10,000 feet.
The bag works with any sleeping pad, but the SynergyLink Connectors only attach to Therm-a-Rest pads with ToeHook features—specifically the NeoAir series and some foam models. Without the connectors, the bag functions like a traditional mummy bag. The attachment system prevents the bag from sliding off the pad during the night, which is especially useful on angled terrain or when you move around in your sleep.
Fill power measures how much space one ounce of down occupies. Our 900-fill down creates more loft per ounce than 650-fill, so we use less total down to achieve the same warmth. This makes the Hyperion 20 lighter and more compressible than a comparable 650-fill bag rated to the same temperature. The tradeoff is cost—higher fill power down is more expensive to source and process.
We strongly recommend a front-loading machine. Top-loaders with center agitators can tear the delicate 10-denier shell fabric and create uneven stress on the baffles. If you only have access to a top-loader, hand wash the bag in a bathtub instead. Fill the tub with cool water and down-specific detergent, gently press the bag to work soap through the fill, then drain and refill several times until the rinse water runs clear.
Regular length fits sleepers up to 6 feet tall. Long length accommodates users up to 6 feet 6 inches. Measure from the top of your head to your toes and add 4-6 inches for the hood and foot box. If you're right at the cutoff height, consider whether you prefer a snug mummy fit or extra wiggle room. Taller sleepers often size up even if they technically fit the regular length.
The 20°F comfort rating assumes you're sleeping in base layers. Adding a puffy jacket, insulated pants, and a warm hat can extend the usable range down to 5-10°F for most sleepers. We've had testers use the bag comfortably at single-digit temperatures with a full sleep clothing system and a well-insulated pad underneath. Beyond that, consider our zero-degree bags for dedicated winter use.
Yes, every Hyperion 20 includes an ultralight nylon stuff sack sized for maximum compression during transport. We also include a larger mesh storage bag for long-term storage at home. Always store your bag in the mesh bag between trips to preserve loft—leaving down compressed for months damages the fill clusters and reduces the bag's warmth over time.