Sea to Summit Spark 15 Review

We brought this 15°F bag into the cold, windy Sierra Nevada's above 6,000 feet in late October, and it was one of the most comfortable nights' sleep in the backcountry we've ever had.

Warmth

The Spark kept us toasty in sub-30°F temperatures, and even when the whipping October winds crept into our floorless tent (and again when our tent collapsed on us at 2AM, so it's even great for cowboy camping). The Spark is an 850+ fill power, PFAS-free, ultra-dry goose down sleeping bag with great loft and good insulation. It kept us warm throughout most of the night, though later in the night we did feel a slight chill below the waist. Still, considering the weather conditions, we were impressed by the amount of warmth it provided.

Weight

The Spark weighs in at 16.9 ounces (or a little over a pound), making it one of the lightest bags we've tested, and putting it in the running with other ultralight bags. We hardly noticed the extra weight in our pack, which made the long miles and switchbacks much more bearable than hiking with heavier bags.

Comfort

The Spark 15 is one of the roomiest, most comfortable bags we've tested that doesn't sacrifice too much warmth. The shell and interior are made with silk-like 10D nylon that feels soft and smooth to the touch. The fabric also isn't incredibly loud when you toss and turn in it, unlike other bags, so we slept like a baby. That said, we're a bit skeptical of how fragile this material is, and took extra measures to keep it away from sharp or rough objects, which can be tough in a backcountry setting.

As people who often toss and turn in our sleep, we love how spacious this bag is. The regular-sized bag we tested is 53 inches in the waist and 61 inches around the shoulders, which is plenty of space to move around while still maintaining its ultralight status. We think that even those with broad shoulders will be happy with the fit. We also appreciate the angled footbox that allows our feet to rest in a natural position. While this is great for back sleepers, it doesn't help as much for side or stomach sleepers—but it's still more comfortable than having our feet resting completely upright. Thanks to the spacious 40-inch footbox, we were able to stretch out a bit rather than feeling like our feet were tied together (as is often the case with other mummy bags).

Packability

We measured the packed size of this bag to be just 7 liters (roughly the size of a camping pot), which barely took up much space at the bottom of our pack, allowing plenty of room for other items.

Features

This bag isn't particularly feature-rich and keeps its design fairly simple and focused on optimizing warmth. It has a full box baffles, meaning that there's no synthetic materials mixed in with the goose down which optimizes warmth and loft. There's a draft tube along the side of the bag and a collar that seals in heat and keeps cold and wind out, which is likely why we didn't feel any wind penetrating the bag throughout the night. The hood cinches just like most other bags we tested, and kept our heads warm throughout the night. We were easily able to fit mid-sized camping pillows into the hood, but our 17-inch wide inflatable camping pillow was quite difficult to squeeze in.

One con of this bag is that its zipper doesn't end all the way at the footbox, so it can't be opened up all the way to be used as a quilt in warmer conditions to allow maximum airflow.

Sea to Summit claims that this bag is made with a water-resistant hood and foot box, and while it's good for fending off morning dew, we didn't find it to be incredibly effective against wet dogs. The marketed “anti-snag” zipper also snagged several times.

Should You Buy the Sea to Summit Spark 15?

The Sea to Summit Spark 15 is an exceptionally comfortable, ultralight sleeping bag that's great for windy, high altitudes. It's one of the best options we tested for those long 10-20 mile days where cutting out weight is essential. However, it's not meant for backpacking in warmer places. And, if you're only planning a 2-day backpacking trip with shorter mileage, there are more affordable sleeping bags that will keep you just as comfy and warm—but they will weigh more.

What Other Backpacking Sleeping Bags Should You Consider?

If you love the Sea to Summit Spark 15 but want a little extra fill power and a zipper configuration that can unzip into a quilt or unzip from both sides to free up your arms to perform tasks inside the tent, the Sea to Summit Spark Pro is an option (though we haven't tested this version just yet).