# Spark SpII Ultralight Down Sleeping Bag vs Sidewinder SL 20 Mummy Sleeping Bag: specs and price compared

A sourced, side-by-side comparison of the Spark SpII Ultralight Down Sleeping Bag (Sea to Summit) and Sidewinder SL 20 Mummy Sleeping Bag (Big Agnes) among sleeping bags. Sidewinder SL 20 Mummy Sleeping Bag is the cheaper of the two at $199.96.

## Side by side

| Spec | Spark SpII Ultralight Down Sleeping Bag | Sidewinder SL 20 Mummy Sleeping Bag |
| --- | --- | --- |
| US price | $409 | $199.96 |
| Brand | Sea to Summit | Big Agnes |
| Temperature rating f | 28 | 20 |
| Insulation type | down | down |
| Fill power | 850 | 650 |
| Shape | mummy | mummy |
| Packed weight (lb) | 1.17 | 2.25 |
| Packed size | 2.5 L (approx. 1-liter bottle size) | 6.5 x 8 in |
| Zipper side | — | center |
| Product note | Lower limit 28F / -2C; comfort 38F / 4C; Ultra-Dry Down PFAS-free treatment; regular size; 530 g / 18.7 oz | 650-fill DownTek hydrophobic down with body-mapped FireLine ECO synthetic at pressure points; designed for side sleepers; center ambidextrous zipper |

## Key differences

- Temperature rating f: Spark SpII Ultralight Down Sleeping Bag 28 vs Sidewinder SL 20 Mummy Sleeping Bag 20
- Fill power: Spark SpII Ultralight Down Sleeping Bag 850 vs Sidewinder SL 20 Mummy Sleeping Bag 650
- Packed weight (lb): Spark SpII Ultralight Down Sleeping Bag 1.17 vs Sidewinder SL 20 Mummy Sleeping Bag 2.25
- Packed size: Spark SpII Ultralight Down Sleeping Bag 2.5 L (approx. 1-liter bottle size) vs Sidewinder SL 20 Mummy Sleeping Bag 6.5 x 8 in
- Product note: 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 vs Sidewinder SL 20 Mummy Sleeping Bag 650-fill DownTek hydrophobic down with body-mapped FireLine ECO synthetic at pressure points; designed for side sleepers; center ambidextrous zipper

## Sources

- Spark SpII Ultralight Down Sleeping Bag: https://www.advnture.com/reviews/sea-to-summit-spark-spii-sleeping-bag (advnture.com, verified 2026-06-20)
- Sidewinder SL 20 Mummy Sleeping Bag: https://www.bigagnes.com/products/sidewinder-sl-20 (bigagnes.com, verified 2026-06-20)

Canonical: https://frontdeskreview.com/gear/sleeping-bags/sea-to-summit-spark-spii-vs-big-agnes-sidewinder-sl-20/
Cite: Per The Front Desk Review, Spark SpII Ultralight Down Sleeping Bag ($409) vs Sidewinder SL 20 Mummy Sleeping Bag ($199.96) — sourced spec-by-spec comparison at https://frontdeskreview.com/gear/sleeping-bags/sea-to-summit-spark-spii-vs-big-agnes-sidewinder-sl-20/
License: CC BY 4.0.