Sea to Summit Spark III Review (2026)

Name: Sea to Summit Spark III
Brand: Sea to Summit
Price: 380.00 USD
Availability: InStock
Rating: 9.0 (1 reviews)

The Spark III strips weight aggressively — a partial-length zipper, minimal hood structure, and ultra-thin 10D shell fabric — to hit 1lb 3oz at 850+ fill power, competitive with cottage-industry quilts while remaining a widely stocked, easily returnable mainstream product. It sacrifices some of the full-zipper convenience and structure of heavier bags, but for hikers who want ultralight weight without ordering from a small-batch cottage brand, it's one of the most accessible options.

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$380 retail

9.0

/10

TrailCraft Score

What Works

1lb 3oz is genuinely competitive with cottage-industry ultralight quilts
850+ fill power down delivers excellent warmth-to-weight ratio
Widely available at major retailers, unlike many ultralight cottage brands
Compresses to a very small packed size

Limitations

Partial-length zipper reduces venting flexibility versus full-zip bags
10D shell fabric is delicate, requiring careful handling
Minimalist hood offers less structure than heavier mummy bag designs
28°F rating limits it to 3-season use for most sleepers

Specifications

Fill Power850+ fill power down

Weight1 lb 3 oz / 538 g

Temp Rating28°F comfort

ZipperPartial-length, ultralight zipper

HoodMinimalist hood with drawcord

Shell10D ripstop nylon

WarrantyLimited lifetime

OriginDesigned in Australia, made in Vietnam

Score Breakdown

Warmth

9.2

Weight / Compression

9.3

Build Quality

9.1

Value for Money

6.5

Brand & Warranty

9.1

What Sets It Apart

It sacrifices some of the full-zipper convenience and structure of heavier bags, but for hikers who want ultralight weight without ordering from a small-batch cottage brand, it's one of the most accessible options.

1lb 3oz, $380 — genuinely ultralight from a widely available mainstream brand

Who This Is For

The Sea to Summit Spark III is right for hikers whose priorities match its design: built around ultralight mainstream down bag, at 1 lb 3 oz and $380.

A note on pricing and links: Prices listed are current as of July 2026 and may change. Some links on this page are affiliate links — if you buy through them, I earn a small commission at no extra cost to you. It does not change my ranking.

How It Compares

See the full sleeping bag comparison

All options in this category ranked side by side — specs, scores, and pricing.

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Common Questions

How does the Spark III compare to cottage-industry quilts on weight?

It's genuinely competitive — 1lb 3oz rivals many cottage-industry quilts from brands like Enlightened Equipment or Katabatic, while being available through major retailers with standard return policies.

Why does the Spark III have a partial-length zipper?

Reducing zipper length is one of several weight-saving measures Sea to Summit used to hit an aggressive weight target, trading some venting flexibility for meaningfully lower overall bag weight.

Is 28°F warm enough for 3-season backpacking?

For most 3-season conditions down to freezing, yes, though cold sleepers or trips with colder-than-expected nights may want a bag liner or warmer layers as backup.