Spark Ultralight Sleeping Bag

So light and tiny you might think you left it at home

$229.00 – $549.00

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Sleeping Bag Temperature Ratings Explained

The EN Rating scale is a scientific test to determine the warmth of a sleeping bag. Unisex sleeping bags list the Lower Limit which is the lowest temperature rating that an average male sleeper would be comfortable in. Our women’s sleeping bags list the Comfort Limit, which is the lowest temperature rating at which an average female sleeper should be comfortable. The comfort and lower limit temperature ratings are listed in the features table on the product page.

For example, a unisex sleeping bag that shows a Lower limit of 23ºF means a man should be comfortable down to air temperatures of 23ºF. The same bag will also have a Comfort limit, in the realm of 32°F, so a woman would be comfortable down to an air temperature of 32ºF. Men and women should always sleep in a layer of long underwear and use 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.

Here’s a basic categorization of appropriate use, based on rated temperatures:
Summer:   >+35ºF / +3°C
3-Season:   +10 to +35ºF / -15° to 0°C
Winter:   <10ºF / -15°C

A huge variety of factors can impact sleeping bag warmth - the above temperatures are merely guidelines, not guarantees. It’s important to think of a sleeping bag as one element in a sleep system which also includes an appropriately insulating sleeping pad and a liner. For instance - 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 nights, plus a sleeping mat with an R-Value of 2.5 to 3, and consider a Reactor thermal liner. If you have any questions about which temperature sleeping bag / R-Value sleeping mat you should select, or how to improve your warmth in a sleep system, reach out to us via our contact page any time.


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Light in weight but heavy in features, the Spark™ Series of down sleeping bags are for the ultralight, gram counting adventurer. The SpI is ideal in summer, SpII will take you through cool summer to fall, and the SpIII is perfect for spring, summer and mild winter adventures. Filled with 850+ loft RDS certified ULTRADRY Down™ and employing an ultra-light 10D Nylon Shell, 1/2 #3 YKK® side zipper and narrow cut, the Spark bags are highly compressible and incredibly light. The Spark SpI packs to the size of a grapefruit making these the perfect option for any ultra-light or minimalist adventures.


Packed Size Comparison

50°F: 1.55L ≈ Like a grapefruit - fits in the palm of your hand
40°F: 2.9L ≈ Two grapefruits
28°F: 3.7L ≈ Loaf of sliced bread


50°F: 12.3 oz ≈ Two tubes of toothpaste
40°F: 16.4 oz ≈ Pint of ice cream
28°F: 22.0 oz ≈ 20oz cup of coffee


50°F: Warm Weather only! Late spring through early fall will be the limits of this bag without a liner.
40°F: 2.5 Season - take this sleeping bag out late spring into early fall, no matter where you are.

28°F: 3 Season - take this bag out in fall, winter and spring.


Slim, there's not a lot of extra room for wiggling.


  • RDS ULTRA-DRY Down 850+ Loft 90% Down Cluster Premium Goose Down
  • Shell: 10D UL Nylon
  • Liner: 15D Nylon soft touch, high-density weave
  • 1/2 length YKK® #3 zipper (Sp II and Sp III have a draft tube)
  • Sp I: Sewn-through construction. Sp II: Box-wall baffle construction in the torso, sewn through in the leg area. Sp III: Box-wall baffle construction throughout
  • Anatomically tapered foot box
  • Includes lightweight Ultra-Sil Nano™ compression bag and a combined storage cell/laundry bag