Therm-a-Rest Saros 20F Sleeping Bag
The Saros 20F is our go-to three-season synthetic sleeping bag for backpackers who refuse to compromise on warmth or weight. Designed to keep you comfortable in temperatures down to 20°F, it combines eradicLOFT™ synthetic insulation with our SynergyLink™ Connectors system, which eliminates the cold spots and shifting that plague traditional mummy bags.
We built the Saros 20F with a thoughtful blend of recycled and solution-dyed fabrics that reduce environmental impact without sacrificing performance. The zoned insulation places more fill where you need it most—across your core and feet—while strategic reduction along the back saves weight and prevents compression. Whether you're chasing alpine sunrises or settling into a desert campsite, the Saros 20F adapts to your body and your sleeping pad for restorative sleep in the backcountry.
Construction & insulation details
SynergyLink™ Integration System
Traditional sleeping bags shift and bunch during the night, creating cold air pockets between you and your pad. Our SynergyLink™ Connectors solve this by securing the Saros 20F directly to compatible Therm-a-Rest sleeping pads through reinforced loops at the shoulders and hips.
The system transforms bag and pad into a unified sleep system—you move, they move together. No more waking up on bare ground with your bag twisted sideways. The connectors work with any pad featuring ToeHook™ loops or our universal SynergyLink™ attachment points, turning two separate pieces of gear into a cohesive sleep platform that stays put all night.
eradicLOFT™ Synthetic Insulation
We developed eradicLOFT™ specifically for conditions where down fails. This continuous-filament synthetic insulation maintains 85% of its thermal efficiency when wet, unlike down which clumps and loses all insulating power.
The fibers are engineered to trap dead air in microscopic pockets that resist moisture penetration. When you’re camping in the Pacific Northwest drizzle or the Smokies’ humid summer nights, the Therm-a-Rest Saros 20F sleeping bag keeps working even after your tent takes on condensation. The insulation compresses for packing but springs back to full loft within minutes of unpacking, providing consistent warmth night after night.
Zoned Insulation & Toe-asis™ Foot Box
Not all parts of your body need equal insulation. We place 20% more eradicLOFT™ fill across the chest, hips, and feet where heat loss occurs fastest, while reducing fill along the back and sides where your pad already provides an insulation layer.
The Toe-asis™ Foot Box adds an extra three inches of width at the feet, allowing your toes to rest in their natural position rather than being forced into a cramped point. This design detail improves circulation and prevents the cramping that wakes you at 3 a.m. in standard mummy bags. Cold sleepers often add a Questar 20 to their quiver for winter trips where down’s weight advantage outweighs moisture concerns, but the Saros remains the workhorse for variable conditions.
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Common Questions About the Saros 20F
The EN 13537 Comfort Rating for the Saros 20F is 28°F, meaning most sleepers will be comfortable at that temperature in base layers. The Lower Limit rating of 20°F represents the coldest temperature at which a cold sleeper can get a full night's rest.
Your personal comfort depends on factors like metabolism, what you ate for dinner, sleeping pad R-value, and campsite exposure. Cold sleepers should add 10°F to comfort ratings as a safety margin.
The Saros 20F works as a standalone bag with any sleeping pad. The SynergyLink™ Connectors are compatible with Therm-a-Rest pads that have ToeHook™ loops or SynergyLink attachment points—most of our NeoAir, ProLite, and Trail series pads.
If your pad lacks these features, the bag still functions perfectly well; you simply won't get the integrated system benefit. The connectors don't restrict use with other pads.
Machine wash on gentle cycle with cold water and technical gear detergent like Nikwax Tech Wash. Tumble dry on low heat with tennis balls to break up clumps and restore loft. Never use fabric softener or bleach.
Store the bag loosely in the included mesh storage sack, never compressed. Hanging it in a closet works too. Compressed storage permanently damages synthetic insulation's ability to loft and retain warmth.
Both bags have the same temperature rating and use eradicLOFT™ insulation. The Parsec 20F offers a roomier cut with more shoulder and hip space, making it ideal for side sleepers and those who prefer less restriction.
The Saros 20F uses a more traditional mummy taper to save weight and improve thermal efficiency. The Parsec weighs about 4 ounces more but provides noticeably more room for movement during sleep.
Yes, if you purchase one right-zip and one left-zip Saros 20F, they can be zipped together to create a double bag. The zippers are compatible across the entire length.
Keep in mind that doubling bags creates gaps along the seams that reduce overall warmth. Two-person use works best in temperatures well above the bag's rating, typically 35°F and warmer.
Synthetic insulation like eradicLOFT™ retains approximately 85% of its warmth when wet, while down loses nearly all insulating ability once saturated. In consistently damp environments—Pacific Northwest, Southeast summer humidity, tropical climates—synthetic is the safer choice.
Down wins on weight and packed size for dry, cold conditions. Many backpackers own both: synthetic for wet-prone trips and down for alpine environments where moisture management is easier.
At 6'0" you're at the upper limit of the Regular size. If you sleep stretched out or prefer extra foot room, size up to Long. If you typically curl up or want to save 5 ounces of pack weight, Regular will work.
The Long adds two inches of packed length but ensures you won't be pressed against the foot box. Most 6-footers choose Regular, but taller torsos or longer legs benefit from the Long size.