Spark™ Ultralight Sleeping Bag

FIVE VERSIONS for performance in any season

$229.00 – $549.00

What Is This

Sleeping Bag Temperature Ratings Explained

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 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. 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 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 for the designed end-use.

Ultralight does not mean ultra-tight: The Spark sleeping bags are snug but still have adequate girth for the performance-oriented backcountry user.

Is this down sleeping bag…?

  • Suitable for cooler temperatures? Yes. You would want the Spark 5°F or possibly the 18°F – either bag will work in late Fall, the 5°F will take you down to winter temperatures when paired with an adequately insulating sleeping mat like the Comfort Light Insulated.

  • Really suitable as a sleeping bag liner? Yes. You could use the Spark 50°F, or even the Spark 40°F or 28°F to boost the performance of a bag for cold-weather use. Adding one of these to a 20°F / -5°C bag might make more sense than buying a “0°F / -20°C” bag for only occasional winter use.

  • Able to be zipped to another sleeping bag? No. Even though the 18°F or 5°F have full-length side zippers, they are not designed to be coupled to a sleeping bag with a right zipper (for instance the Flame 18°F or 5°F).

Read up on the factors which define and affect down quality, and what they mean for you as an end user HERE 


Best Use

  • Ultralight Backpacking, Bike Touring, Liner Bag


  • Summer or Sleeping Bag Liner: 50°F  (comfort range 50°F to 70°F)
  • Warm weather: 40°F (comfort range 40° to 60°F)
  • 2 Season: 28°F (comfort range 28°F to 60°F)
  • 2.5 Season: 18°F (comfort range 18°F to 55°F)
  • 3.5 Season: 5°F (comfort range 5°F to 50°F)


  • ULTRA-DRY Down 850+ Loft 90% Down Cluster Premium Goose Down certified Responsible Down Standard (RDS)
  • 10D shell and 7D liner materials help to achieve the incredible lightweight and compact packed size
  • Includes lightweight Ultra-Sil™ compression bag and storage cell
  • Zipper-length trimmed for gram-saving performance
    • 50°F, 40°F, and 28°F have 1/3-length zippers
    • 18°F and 5°F have full-length side zippers
  • Baffle construction
    • 50°F and 40°F have sewn-through construction.
    • 28°F has baffles in the torso and sewn through in the leg area.
    • 18°F and 5°F are fully baffled.