Kelty Cosmic Synthetic Fill 40 Degree Backpacking Sleeping Bag with Compression Straps, Compact and Lightweight, 2022
Best for
Best with strap system
Amazon rating
Amazon aggregate, one input among many in the Verdict Score
Based on 3 trusted sources
Current price
$87.00
Updated May 18, 2026 · 1 min read
Sources behind this verdict
10 reviewers weighted by source trust
The consensus
What reviewers found
Synthesized across the trust-weighted source mix below.
Across the reviewers we read, the Kelty Cosmic Synthetic 40 is the synthetic counterpart to the Cosmic Down 40 and trades packed volume for a lower price and easier care. rockrunner.net and treelinebackpacker.com both treat the Cosmic 40 family as a budget three-season option with a useful draft collar and roomy mummy fit; the synthetic version inherits the cut but uses CirroLoft fill, which Kelty pairs with an integrated compression stuff sack to claw back some packed-size disadvantage. r/CampingGear users describe it as roomy enough for side sleepers and praise the two-way zipper for ventilation on warmer nights — a genuine summer-use feature.
What reviewers liked
- r/CampingGear users praise the roomy mummy cut and two-way zipper for summer ventilation
- Integrated compression straps and stuff sack help with packing per retailer descriptions on amazon.com
- Strong verified-purchase rating (4.6/92) and brand reputation per rockrunner.net and treelinebackpacker.com
Where it falls short
- r/Ultralight users say the synthetic fill packs noticeably larger than down at the same rating
- Multiple Reddit threads recommend swapping the included stuff sack for an aftermarket compression sack
- Synthetic insulation is heavier than down competitors in this price band, per community consensus
Across the reviewers we read, the Kelty Cosmic Synthetic 40 is the synthetic counterpart to the Cosmic Down 40 and trades packed volume for a lower price and easier care. rockrunner.net and treelinebackpacker.com both treat the Cosmic 40 family as a budget three-season option with a useful draft collar and roomy mummy fit; the synthetic version inherits the cut but uses CirroLoft fill, which Kelty pairs with an integrated compression stuff sack to claw back some packed-size disadvantage.
r/CampingGear users describe it as roomy enough for side sleepers and praise the two-way zipper for ventilation on warmer nights — a genuine summer-use feature. r/Ultralight is more critical: multiple commenters say the bag packs larger than they'd want for serious backpacking and that synthetic 40°F bags in this price band generally aren't competitive on weight against down. r/WildernessBackpacking reviewers specifically recommend buying a separate compression sack.
The consensus is that this is a strong car-camping and short-trip summer bag, especially for buyers who want compression straps built in and don't want to pay for down. It's not the pick for gram-counters.
- 20D Nylon Taffeta Shell, 50D Taffeta Liner, Cirroloft Synthetic Fill
- Imported
- 40 Degree Temp Rating, Regular Size
- Fits sleepers up to 6ft, fill weight 24oz, total weight 2lbs 6oz, stuff size (non-compressed) 15x8 inches. Color: Duffel Bag Green/Smoke
- Packability
- Integrated compression stuff sack, coupled with the premium packability of the synthetic fill allow the Cosmic synthetic to reach minimalist standards of backpacking gear. Trail weight varies by temp rating, from 2lbs 6oz to 4lbs 11oz.
- Insulation
- Cirroloft synthetic insulation provides reliable warmth in cold and damp conditions, maintains loft for even coverage with no cold spots. Temperature ratings from 0 degrees to 40 degrees, to ensure your time on the trail is comfortable.
- Tailored Fit
- Natural fit spacious footbox gives more room to wiggle your toes, and length options range to fit sleepers 5’8” to 6’6”. A handy stash pocket on the exterior of the bag for your overnight goodies and essentials in the tent.
- Kelty Craftsmanship
- Kelty is synonymous with quality in the outdoor community. Kelty gear is built for play, and built to last. The Cosmic Synthetic bag is ready to be put through the ringer on the trail, campground, and everywhere in between.
It's roomy and comfortable for side sleeping. The two-way zipper is great for ventilation. Packs up pretty small without a compression sack, at ...
My wife has one. It's fine. I recommend a compression sack as it packs down Brett big in the bag it comes with.
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“Kelty Cosmic Synthetic Sleeping Bag Series Review” · YouTube
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