Sea to Summit Spark Sp III

Premium materials and efficient design give this three-season bag one of the best warmth-to-weight ratios we’ve seen.

Brand: Sea to Summit

Model: Spark Sp III Sleeping Bag


We pushed this bag in wet conditions that challenged its temp rating. During an all-night storm in a tiny tent in Wyoming’s Wind River Range, we woke up to a sopping wet fly pressed against the lower half of our bags. Despite the damp footbox shell, our bare feet never got chilled, even with temps in the upper 20s. The warmth comes from 850-fill, water-resistant goose down that’s strategically distributed to maximize efficiency. Fifty-five percent of the bag’s overall fill resides in the top—with more concentrated around the core, where you need it. This design reduces the amount of down compressed underneath you (which doesn’t provide any insulation when flattened), while still maintaining a low overall weight. The contoured hood fits well.


The wispy, 10-denier Pertex Quantum shell and ¹/3-length zipper keep weight down. Be careful though: We managed to rip a 1/16-inch hole in the draft tube after (frustrated) yanking on a snagged zipper. Thanks to the ultralight fabrics and short zipper, it compresses to an extraordinarily small 9 by 5 inches. However, that short zip limits venting; we used it as more of a quilt in warm, humid conditions.


At only 57 inches at the shoulders, the fit is on the trim side, so larger folks and restless sleepers may favor a roomier bag.

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