The Thermarest Hyperion 20 UL Down Sleeping Bag has become a benchmark in the ultralight backpacking world. Designed for those who want to cut weight without sacrificing warmth, it combines premium materials, clever construction, and a minimalist approach to deliver one of the lightest three-season sleeping bags available. This review explores its design, performance, durability, and value, offering a clear picture of whether it suits your style of adventure.
Design and Build Quality
The Hyperion 20 is built with a 10D nylon ripstop shell treated with a durable water repellent (DWR) finish. Inside, it uses 900-fill Nikwax Hydrophobic Down, which resists moisture and maintains loft up to 60 times longer than untreated down. This is a critical feature for ultralight gear, as damp down can quickly lose insulating power.
The bag employs box-baffled construction, which prevents cold spots by allowing the down to loft evenly. Thermarest has also zoned the insulation, placing 70% of the fill on the top and sides, and 30% on the back. Since much of the underside insulation is compressed against a sleeping mat, this design saves weight without compromising warmth.
Another standout feature is the SynergyLink™ Connector system. These lightweight straps attach the bag to your sleeping pad, preventing you from sliding off during the night. They can be removed if you prefer a more traditional setup.
Weight and Packability
At just 594g for the regular size and 640g for the long, the Hyperion 20 is among the lightest sleeping bags in its temperature class. The packed size is impressively small at 15 x 20 cm, making it easy to fit into compact packs. For fast-and-light backpackers, bikepackers, and alpinists, this weight-to-warmth ratio is a major advantage.
The included compression sack further reduces bulk, while a larger storage sack is provided for long-term loft preservation.
Temperature Ratings and Warmth
The Thermarest Hyperion 20 UL Down Sleeping Bag 20 is EN-rated with a comfort rating of 0°C, a comfort limit of -6°C, and an extreme rating of -23°C. In practical terms, most users will find it comfortable down to around freezing, with the ability to push lower when paired with a quality insulated sleeping pad and layered clothing.
The ThermaCapture™ lining reflects radiant body heat back towards the sleeper, adding warmth without extra weight. Combined with the high fill power down, this makes the bag feel warmer than many competitors of similar weight.
Fit and Comfort
The Hyperion 20 has a mummy shape with an ergonomic cut that balances efficiency with comfort. The shoulder girth is 145 cm, tapering to 109 cm at the foot. While this trim design reduces dead air space and improves thermal efficiency, it may feel restrictive for broader-shouldered sleepers or those who prefer more room to move.
The half-length zip is another weight-saving feature. It reduces bulk and heat loss but limits venting options in warmer conditions. For those who often camp in variable climates, this could be a drawback.
Performance in the Field
In dry, cold conditions, the Hyperion 20 excels. The down lofts quickly, the bag feels warm almost immediately, and the lightweight construction makes it easy to carry on long treks. The hydrophobic down provides peace of mind in damp environments, though like all down bags, it still requires careful handling to avoid saturation.
The SynergyLink™ straps are particularly useful on uneven ground, keeping the bag aligned with the mat. However, some users find them fiddly or unnecessary, and they can be removed to save a few grams.
Durability
The 10D nylon shell is lightweight and contributes to the bag’s ultralight status, but it is thinner than heavier-duty fabrics. While it holds up well under normal use, it requires care to avoid snags or tears. Using a tent, bivy, or groundsheet is recommended to extend its lifespan.
The down is Responsible Down Standard (RDS) certified, ensuring ethical sourcing. With proper care and storage, the bag should maintain loft and performance for many years.
Pros and Cons
Pros
- Extremely lightweight for its warmth rating
- Premium 900-fill Nikwax Hydrophobic Down
- Compact packed size
- Zoned insulation for efficiency
- SynergyLink™ straps keep bag aligned with mat
- Excellent warmth-to-weight ratio
Cons
- Narrow cut may feel restrictive for some
- Half-length zip limits ventilation
- Thin shell fabric requires careful handling
- Less versatile in warmer climates
Value for Money
The Hyperion 20 sits at the premium end of the market, but its performance justifies the price for those who prioritise ultralight gear. Compared to heavier alternatives, it allows significant weight savings without compromising on warmth, making it a worthwhile investment for serious backpackers and mountaineers.
For casual campers or those who prioritise comfort and space over weight savings, a more spacious and less expensive bag may be a better fit. But for fast-and-light adventurers, the Hyperion 20 is one of the best options available.
Final Verdict
The Thermarest Hyperion 20 UL Down Sleeping Bag is a specialist piece of gear designed for those who demand maximum warmth for minimum weight. It shines in alpine missions, long-distance treks, and ultralight setups where every gram counts. Its premium down, clever construction, and compact pack size make it one of the most efficient sleeping bags in its class.
It does come with trade-offs: a snug fit, limited ventilation, and delicate materials. But for the right user, these are acceptable compromises for the performance gains. If your priority is cutting weight without sacrificing warmth, the Hyperion 20 is a standout choice.
