BEST USE: Ultralight Backpacking
PERFORMANCE: 2 Season
WEIGHT: 1lb 1.3oz | 490g
COMPRESSED VOLUME: 2.5 liters
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The EN Rating scale is a scientific test to determine the warmth of a sleeping bag. The test produces a Lower rating (for male sleepers) and a Comfort rating (for female sleepers). Both are listed in the features table on the product page.
A unisex sleeping bag with a Lower limit of 14ºF means a man should be comfortable down to air temperatures of 14ºF. The same bag will also have a Comfort limit, in the realm of 27°F, so a woman would be comfortable down to an air temperature of 27ºF. These ratings require a sleeping mat with an R-Value appropriate for expected ground temperatures – without this, the sleeping bag itself is unlikely to keep the sleeper warm enough.
A variety of factors impact sleeping bag warmth - the above temperatures are merely guidelines, not guarantees. It’s important to think of a sleeping bag, an appropriately insulating sleeping pad and a liner as a sleep system. For example - if you plan on sleeping in nighttime air temperatures of 27ºF / -3°C, choose a bag with a gender-appropriate rating of 23°F / -5°C, plus a sleeping mat with an R-Value of 2.5 to 3, and consider a Reactor thermal liner.
The Spark Ultralight Mummy Sleeping Bag Series spans everything from an ultralight down-filled liner, to a mid-winter fast-and-light sleeping bag. Each model uses premium materials and no-frills design to provide cutting-edge performance.
Ultralight does not mean ultra-tight: The Spark mummy sleeping bags are snug but still have adequate wiggle room for the performance-oriented, backcountry user.
Best UseUltralight Backpacking
Comes WithUltra-Sil compression bag and storage cell
InsulationUltra-Dry Down 850+ Loft
Shell FabricUltralight 10D Nylon Shell
Zip OptionsSpark 0-II: Left-side #3 YKK zipper; Spark III-IV: #5 YKK
|Spark I (5°C) Regular
|Spark I (5°C) Long
|Spark II (-2°C) Regular
|Spark II (-2°C) Long
|Spark III (-8°C) Regular
|Spark III (-8°C) Long
|Spark IV (-15°C) Regular
|Spark IV (-15°C) Long
The second highest-lofting down used in any of Sea to Summit’s sleeping bags or quilts. 850+ Fill Power indicates that one ounce (30g) of down will re-expand to over 850 cubic inches after compression. Higher loft means that less down can be used to achieve the same temperature rating – important for performance sleeping bags. The loft and down quality/composition are independently tested by the International Down and Feather Laboratory (IDFL) – a copy of the certification is supplied with every Sea to Summit sleeping bag. The down is responsibly sourced and RDS certified and treated with our non-PFC Ultra-Dry Down™ treatment.
100% of the down used in our sleeping bags and quilts is independently certified to the Responsible Down Standard (RDS). The RDS certifies down against animal welfare requirements and tracks it from the source to the final product. The purchase of RDS certified products demonstrates demand for better animal welfare practices in the down and feather supply chain. Sea to Summit is certified to the RDS. To learn more about RDS visit
Despite being incredibly lightweight, the 10 Denier UL Nylon is down-proof and surprisingly durable. A DWR finish helps to shed external moisture. This fabric is part of the secret to making the Spark and Flame Down Sleeping Bag Series some of the lightest, most packable sleeping bags available today.
Sea to Summit hydrophobic down and DWR finishes are Non-PFC.
The down is RDS-certified responsibly sourced. The non-PFC Ultra-Dry Down™ hydrophobic treatment means it absorbs less water than untreated down and dries much more quickly. Ultra-Dry Down does not affect the loft or lifespan of the down, or its breathability. The treatment will last through at least 20 washings
Non-PFC DWR Shell fabric:
Despite being incredibly lightweight, the 10 Denier UL Nylon is down-proof and surprisingly durable. A non-PFC DWR finish helps the shell to shed external moisture. This fabric is part of the secret to making the Spark and Flame Down Sleeping Bags and the Ember Quilt Series some of the lightest, most packable sleep system products available today.
Frequently Asked questions
Suitable for cooler temperatures?
Yes. The -15°C or possibly the -8°C will work in late Autumn. The Spark -15°C will take you down to winter temperatures when paired with a greater than 3.5 R-Value sleeping mat like the Comfort Light Insulated.
Really suitable as a sleeping bag liner?
Yes. You could use the Spark 10°C, or even the Spark 5°C to boost the performance of a bag for cold-weather use. Adding one of these to a -6°C bag might make more sense than buying a -17°C bag for occasional winter use.
Able to be zipped to another sleeping bag?
No. Even though the -8°C or -15°C have full-length side zippers, they are not designed to be coupled to a sleeping bag with a right zipper (for instance the Flame)