Kelty Cosmic Synthetic Sleeping Bag 40F
- 40 F rating
- 2 lb 6 oz total, 24 oz fill
- Fits up to 6 ft (regular)
- Cirroloft synthetic insulation
- Compression stuff sack integrated
- 20D nylon shell, 50D liner
Last refreshed Sep 8, 2026 · Based on the Amazon listing and published specifications, not hands-on testing.
A light synthetic mummy for warm weather backpacking that holds warmth when damp. It is a summer bag, so cold nights need a warmer rating.
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ASIN: B082P5VGGTModel: Cosmic Synthetic 40Category: Sleeping Bags
Colors Available
Sizes Available
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Overview
Synthetic Cirroloft fibers keep their loft when damp, giving even warmth without down's moisture worries. A mummy cut with a natural fit footbox and an integrated compression sack makes it trail ready.
Damp weather reliability and a light weight suit summer backpacking. The warm rating limits it to mild nights.
Who it's for
Warm weather hikers and campers in humid areas suit this bag. Shoulder season campers should look at the colder rated versions.
Pros and cons
- Light for a synthetic bag
- Warm when damp
- Compression stuff sack
- Exterior stash pocket
- Warm weather rating only
- Bulkier than down
- Weight listed two ways
Performance notes
Synthetic fibers trap air even when damp, so warmth drops less than down in wet conditions. A mummy cut limits air to heat. Compression reduces packed volume for the trail.
Specifications
| Brand | Kelty |
|---|---|
| Model | Cosmic Synthetic 40 |
| Dimensions & fit | |
| Maximum Height Recommendation | 6 feet |
| Item weight | 2 lb 6 oz |
| Fill weight | 24 oz |
| Item Dimensions L x W | 78 x 31 inches |
| Stuff size | 15 x 8 inches (non-compressed) |
| Capacity & performance | |
| Temperature Rating | 40 F |
| Construction & materials | |
| Fill Material Type | Cirroloft synthetic |
| ShellMaterial | 20D nylon taffeta |
| Material | 50D taffeta liner |
| Included components | |
| Included Components | Sleeping bag, compression stuff sack |
| Warranty & support | |
| Warranty Description | Limited |
| Other details | |
| Shape | Mummy |
Frequently asked questions
How small does the Kelty Cosmic Synthetic 40 pack?
The stuff size is 15 x 8 inches non-compressed, and the integrated compression sack shrinks it further.
What height fits the regular Cosmic Synthetic?
Sleepers up to 6 feet. Other lengths fit sleepers from 5 feet 8 to 6 feet 6.
Does the Kelty Cosmic Synthetic stay warm when wet?
Cirroloft synthetic insulation provides warmth in cold and damp conditions.