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).
Specs:
