Construction & Features

Starting with the materials, we really like what the Sea to Summit Spark Pro Sleeping Bag has going on. Its 950 fill power RDS certified down is top shelf and totally best in class. Most high end sleeping bags utilize 850, or 900 fill power, which leaves Spark Pro a cut above. Furthermore, its baffles are generously filled, which makes for a conservative temp rating – we haven’t tested it in conditions this cold, but you likely could sleep comfortably in 15F degrees in the Spark Pro 15. Likely nobody would have batted an eye if they decided to call it the Spark 10.

We also appreciate the use of 10d nylon shell fabric, which saves weight while still offering sufficient durability and comfort. Many mainstream outdoor brands of comparable size to Sea to Summit shy away from thinner shell fabrics, instead opting for 15d or 20d, and thus catering to the lowest common denominator who are more likely to damage their bag. Not so here.

There’s lots of little design touches that make this a great sleeping bag. We nod to the mixed baffles orientation which prevents down drift and cold spots, especially for side sleepers. Also the draft tube, and zipper plow, which seems to never get stuck.

Perhaps the most interesting aspect to the Spark Pro design is the Free-Flow Zip. This network of zipper tracks allows for highly customizable ventilation and even wear-ability. The primary zipper runs on the wearer’s left side from shoulder to knee, and is used for entry/exit, as well as side ventilation. A second zipper track runs from knee downwards and traces the footbox. This allows for foot ventilation on warm nights. Open both of those zippers and you can convert the Spark Pro into a pseudo quilt. A short zipper track located at the right shoulder can be opened allowing the user to stick both arms out while keeping their torso warm.

While the aforementioned zippers do add versatility and massive ventilation capabilities, they also add significant zipper weight, a bit of cold spotting (despite interior zipper insulated flaps), increased cost, more avenues to potential gear failure, and ultimately decrease warmth-to-weight ratio. As such, we view the Free-Flow Zip system as a net negative that degrades the efficacy of the sleeping bag for more ventilation than is necessary and a quilt-mode that people probably won’t use. Or if you do intend to use quilt mode, just buy a quilt instead.