The Sea to Summit Spark II is a mummy style sleeping bag that's designed for the minimalist backpacker who wants to be light and fast on the trail. That's a big reason why I originally purchased it myself. Now that I have trail tested it for over three years in various conditions I will share with you all its features and my overall experience with it.
The Spark SP II is comparable in price to other premium 16oz ultralight sleeping bags like the Western Mountaineering Highlight. There are cheaper ultralight sleeping bags out in the market, but they are made with less durable materials. Click on the links provided for the current price of the Sea to Summit Spark SP II.
The sleeping bag only weighs a mere 16oz (regular size). It achieves this low weight because of its lightweight fabric, slim-cut design, a small 1/3 length zipper, the use of box walled baffles only in the torso area where its needed most, and its insulated with 850+ fill down which gives you an optimal warmth to weight ratio.
Despite the Spark SP II being a minimalist sleeping bag, it is surprisingly warm to sleep in. This is no doubt contributed to the high loft 850+ fill down, but also because of the box walled baffle system as opposed to cheap sewn through construction methods. This prevents cold spots in your sleeping bag.
The Spark SP II is rated as a 35-degree bag. With my personal experience, I would say that's pretty accurate because when the temperatures hit around freezing the sleeping bag startes to struggle to keep me warm. It's a good 3 season sleeping bag, but when it comes to shoulder season trips it will have trouble. To help with this problem Sea to Summit has sleeping bag liners like the Thermolite Reactor which adds about 15 degrees of warmth.
Sea to Summit designed this sleeping bag with high-quality materials. To start with, the Spark SP II uses a thin 10D nylon fabric called Pertex Quantum for its outside shell. If you look closely at the material, it is semi-translucent and you can see the down right through the fabric. This material is perfect for a sleeping bag because it's lightweight, strong, and very breathable. To protect the sleeping bag from moisture the fabric is treated with a durable water repellent.
For the inside liner, the Spark SP II uses a slightly thicker 15D nylon down proof fabric that feels soft to the touch and is durable.
The insulation that's used is a high loft 850+ goose down that has a moisture repelling treatment added to it. This treatment allows the sleeping bag to keep you warm even when it gets a little damp from the condensation in your tent.
I find the Spark SP II to be very comfortable. With soft down and nylon fabric, it feels nice and cozy to sleep in. The one downside with the ultralight sleeping bag is its slim-cut design. You tend to feel a little constricted with little room to be able to shift yourself around. I tend just to roll or twist the entire sleeping bag along with me if I need to move during the night. This is common with most ultralight sleeping bags. It's just something you have to sacrifice in order to be lightweight.
Even though the Spark SP II is a minimalist sleeping bag, it still includes in its design a hood to keep your head warm and comfortable which is not a typical feature for ultralight sleeping bags
The best feature of the Spark SP II has to be the fact that it can pack down to about the size of a grapefruit by using the compression sack that comes with it. With the sleeping bag compressed to that size, you won't have any trouble finding space in your backpack for it.
SPARK II PROS
Compresses down very small
SPARK II CONS
Slim-cut design can make you feel a little constricted
Not good for shoulder season backpacking (Sea to Summit Liner needed)
Overall the Sea to Summit Spark SP II is a great sleeping bag to own. It's super lightweight and packs down very small while still providing you with adequate warmth on your 3 season backpacking trips. The sleeping bag is not without its flaws though, such as it being a little restrictive in its slim-cut design, but to me, this can easily be overlooked because of all the other benefits as stated in this article.
No box wall baffle construction
Box wall baffle construction throughout
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