We’re a staff full of down snobs (no apologies), but for the first time ever, we found ourselves choosing synthetic over feathers on three-season trips down to 30°F—whether or not there was rain in the forecast.
The Spark changed our minds, first and foremost, by disappearing into our packs. It squishes to 7 by 12 inches in the included compression sack—about the same size of a comparably priced down sack. Mountain Hardwear achieved this by welding its proprietary Thermal.Q insulation (longer fibers loft in curlicue shape, while shorter ones fill the spaces between) directly to the inside of the shell, eliminating redundant and bulky shingling. The resulting bag kept us warm to 35°F without so much as a cold spot (and we used it down to an impressive 20°F while wearing a puffy).
Also, the two-way center zip makes it easy to sit up and do basic tent chores without getting all the way out of your bag. In icy weather, we could unzip from the bottom and stick out our little T-rex arms, or in milder temps we could unzip from the top and wear the bag more like a large, insulated cape. Either way, it beats getting out of your bag all at once. Extra credit: The reduced number of seams makes the interior feel like silk sheets against our skin. And that’s something new to be snobby about.