# Cosmic Down 20 Sleeping Bag vs Spark SpII Ultralight Down Sleeping Bag: specs and price compared

A sourced, side-by-side comparison of the Cosmic Down 20 Sleeping Bag (Kelty) and Spark SpII Ultralight Down Sleeping Bag (Sea to Summit) among sleeping bags. Cosmic Down 20 Sleeping Bag is the cheaper of the two at $189.95.

## Side by side

| Spec | Cosmic Down 20 Sleeping Bag | Spark SpII Ultralight Down Sleeping Bag |
| --- | --- | --- |
| US price | $189.95 | $409 |
| Brand | Kelty | Sea to Summit |
| Released | 2024 | — |
| Temperature rating f | 20 | 28 |
| Insulation type | down | down |
| Fill power | 550 | 850 |
| Shape | semi-rectangular | mummy |
| Packed weight (lb) | 2.44 | 1.17 |
| Packed size | 8 x 13 in | 2.5 L (approx. 1-liter bottle size) |
| Zipper side | right | — |
| Product note | 550-fill DriDown; ISO comfort 31F, lower limit 21F; regular weight 2 lb 7 oz | Lower limit 28F / -2C; comfort 38F / 4C; Ultra-Dry Down PFAS-free treatment; regular size; 530 g / 18.7 oz |

## Key differences

- Temperature rating f: Cosmic Down 20 Sleeping Bag 20 vs Spark SpII Ultralight Down Sleeping Bag 28
- Fill power: Cosmic Down 20 Sleeping Bag 550 vs Spark SpII Ultralight Down Sleeping Bag 850
- Shape: Cosmic Down 20 Sleeping Bag semi-rectangular vs Spark SpII Ultralight Down Sleeping Bag mummy
- Packed weight (lb): Cosmic Down 20 Sleeping Bag 2.44 vs Spark SpII Ultralight Down Sleeping Bag 1.17
- Packed size: Cosmic Down 20 Sleeping Bag 8 x 13 in vs Spark SpII Ultralight Down Sleeping Bag 2.5 L (approx. 1-liter bottle size)
- Product note: Cosmic Down 20 Sleeping Bag 550-fill DriDown; ISO comfort 31F, lower limit 21F; regular weight 2 lb 7 oz vs Spark SpII Ultralight Down Sleeping Bag Lower limit 28F / -2C; comfort 38F / 4C; Ultra-Dry Down PFAS-free treatment; regular size; 530 g / 18.7 oz

## What reviewers say

**Cosmic Down 20 Sleeping Bag** — Two whitelisted hands-on testers (CleverHiker, Switchback Travel) reviewed the Kelty Cosmic Down 20 and both call it a strong-value budget 3-season down bag. Both praise its warmth-to-weight ratio, buttery-soft lining, and low price, and both flag it as heavy and bulky for a backpacking-specific bag while noting the large gap between the women's and unisex versions. CleverHiker's tester observed comfortable warmth to 30F against the 20F spec. All six quotes and the one measured value were verified as literal substrings of the fetched source text. (2 sourced reviews.)

## Sources

- Cosmic Down 20 Sleeping Bag: https://kelty.com/products/cosmic-down-20 (kelty.com, verified 2026-06-20)
- Spark SpII Ultralight Down Sleeping Bag: https://www.advnture.com/reviews/sea-to-summit-spark-spii-sleeping-bag (advnture.com, verified 2026-06-20)

Canonical: https://frontdeskreview.com/gear/sleeping-bags/kelty-cosmic-down-20-vs-sea-to-summit-spark-spii/
Cite: Per The Front Desk Review, Cosmic Down 20 Sleeping Bag ($189.95) vs Spark SpII Ultralight Down Sleeping Bag ($409) — sourced spec-by-spec comparison at https://frontdeskreview.com/gear/sleeping-bags/kelty-cosmic-down-20-vs-sea-to-summit-spark-spii/
License: CC BY 4.0.