Head-to-head · Best 0 Degree Sleeping Bags

Sea to Summit Spark 0F vs Therm-a-Rest Parsec 0F/-18C

Which is the better buy? Side-by-side on rating, price, strengths, and watch-outs — with the published ratings we averaged to get there.

The short answer

Therm-a-Rest Parsec 0F/-18C comes out ahead by a narrow margin (4.4 vs 4.5). The gap is mostly about Weight- and budget-conscious winter backpackers who want a genuinely light 0°F down bag and sleep on the warmer side. — read the strengths below before deciding.

Ranked #4 in Best 0 Degree Sleeping Bags

Sea to Summit Spark 0F

4.4

$349as of Jun 8

The Spark 0F is the ultralight of this group, packing a genuine 0°F-rated bag into about 2 lb 7 oz and a sub-10-liter stuff size. It uses 850+ fill Ultra-Dry down and reviewers find its temperature rating accurate. The trade-offs are a snug, less-forgiving cut and a thin shell that offers little wet-weather protection, plus a steep price for the warmth.

Strengths

— Among the lightest 0°F down bags at roughly 2 lb 7 oz
— Sub-10-liter packed size, the most compressible bag here
— 850+ fill power Ultra-Dry treated goose down resists moisture

Watch-outs

— Snug ultralight cut is less forgiving than the Kodiak or Ibis
— Thin shell offers little wet-weather protection
— Pricey at roughly $649-$679 for the warmth delivered

$349 · Buy at seatosummit.com Full review →

Higher ratedRanked #3 in Best 0 Degree Sleeping Bags

Therm-a-Rest Parsec 0F/-18C

4.5

$530

The Parsec 0F is the warmth-to-weight champion of this group, at 2 lb 6 oz one of the lightest true 0°F down bags you can buy. Reviewers across The Trek, Advnture, and SectionHiker praise its loft and value, though it uses 800-fill down and at least one cold-test reviewer found its honest comfort floor closer to 5°F than 0°F. At around $530 it badly undercuts the premium bags here.

Strengths

— Outstanding warmth-to-weight ratio at just 2 lb 6 oz for a 0°F bag
— 800-fill Nikwax Hydrophobic Down resists moisture and dries faster
— Box-baffled, body-mapped 60/40 down distribution puts insulation where it counts

Watch-outs

— Still expensive at $490-$570 in absolute terms
— One real-world cold test recommended a 5°F practical floor, not 0°F
— Cold sleepers and women may find the honest comfort closer to 10°F

$530 · Check Price on Amazon Full review →

How they stack up

Sea to Summit Spark 0F

The lightest and most compressible bag here, undercutting the Therm-a-Rest Parsec 0F on weight and packed size and far lighter than the Western Mountaineering Kodiak MF, Feathered Friends Ibis ES 0 and Mountain Hardwear Phantom 0, but with a snugger cut and a thin, less weatherproof shell.

Therm-a-Rest Parsec 0F/-18C

The lightest and best-value true 0°F bag here, beating the Western Mountaineering Kodiak MF, Feathered Friends Ibis ES 0 and Mountain Hardwear Phantom 0 on warmth-to-weight and price, though it uses lower 800-fill down than the Kodiak and Ibis and is heavier than the Sea to Summit Spark 0F.

Specs side-by-side

Spec	Sea to Summit Spark 0F	Therm-a-Rest Parsec 0F/-18C
Temperature Rating	0°F limit / 14°F comfort	0°F limit / 14°F comfort (ISO)
Fill Power	850+ Ultra-Dry goose down	800 Nikwax Hydrophobic goose down
Fill Weight	29.6 oz (840 g)	—
Total Weight	2 lb 7 oz (1113 g)	2 lb 6 oz (1.09 kg)
Packed Size	9.9 L	—
Shell	Ultralight nylon	—
Zipper	Full-length YKK with draft tube	Two-way YKK side zip
Cut	Snug ultralight mummy	—
Baffles	—	Box-baffled, 60/40 body-mapped
Length	—	Regular 80 in
Extras	—	Pad straps, external quilt loops
Warranty	—	Limited lifetime

← See the full ranking of best 0 degree sleeping bags