Sea to Summit Spark III Review

June 4, 2015
Sea to Summit Spark III
Warmth to Weight Ratio

The Good

  • Lightweight
  • Comfortable hood
  • Great warmth-to-weight ratio
  • Highly compressible

The Bad

  • Poor venting
  • Narrow throughout, especially in torso and upper legs
  • Expensive

The Sea to Summit Spark III earned raves from the ‘light-and-fast’ packers on my test team, thanks to its great warmth-to-weight ratio and it compact nature in the pack. I however, found it a bit restrictive in terms of fit and seasonal versatility. The cut is slim from shoulders to knees, and the short zipper eliminates venting options below mid-torso. The Spark III weighs 8 ounces less than the Montane Minimus, but those ounces come at the cost of sleeping comfort. Still, the Spark III proved ideal for those seeking minimal pack weight and volume.


The Sea to Summit Spark III packs so small, it doubled as rugby ball during one night in camp alongside a snowfield in Central Oregon (the snowfield served as our rugby pitch). The Summit III, when fully compressed, measured about 6- by 9-inches—the smallest packed size of any bag we tested. 

I stayed warm in this bag right down to its listed warmth rating of 25ºF. The Spark III’s warmth is partially due to its slim design. The bag offers no wiggle-room, and therefore, no dead-air spaces to suck up body heat. The Spark, with its 850-fill water-resistent down, held me in a snug cocoon-like embrace that restricted movement, but greatly added warmth. 

The incredible lightweight nature of the Spark III comes in large part thanks to a Spartan-like design. There are no extraneous comfort features to speak of. The main zipper extended less than half my body length. The one winning feature of the bag was its hood. I found the hood comfortable whether left open or cinched snug. When cinched down, the hood stayed in place as I moved—of course, since the bag’s cut limited body movement, the hood didn’t have much chance to move either. 

Overall Comfort
The narrow cut, short zipper, and lack of added features made this a great bag to carry, but severely limited sleeping comfort. I felt very constricted (I’m 6’2” with a 48” chest diameter) though slighter-built hikers also expressed some reservations about the narrow design of the torso area. The short zip also affected comfort during moderate nights when some extra ventilation could have prevented excess heat buildup. The real comfort win for this bag comes in the pack—it packs small and is very lightweight, so I was a bit more comfortable on the trail. 

The Spark III employs a silky 10-denier Pertex Quantum nylon fabric for its shell, which helps keep the overall bag weight down. But that gossamer shell showed wear and tear pretty quickly. I snagged the bag on a rock while unstuffing it outside the tent, and that alone caused a small tear in the foot section. I’d be hesitant to lay out in this bag anywhere except inside a clean tent free of any hard, sharp gear. (NOTE: during that rugby match mentioned in the verdict above, we tucked the stuffed bag it into a second stuff sack for added protection).

The lack of features and comfort means the hefty price is being paid, for just one thing: minimal weight. For light-and-fast hikers, that could be a great value. For general backpackers, though, the price is steep for what they’ll get.


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