Sea to Summit Spark SPI Sleeping Bag Review

I have been in the market for a new, lightweight, treated down sleeping bag for a while.  When I saw the Sea to Summit Spark SPI sleeping bag earlier this year I knew I had to hold out for it.  I’m glad I did because Sea to Summit delivered a fantastic sleeping bag that is exactly what I was hoping for.  Rated at 46° F (8° C) it is perfect for summer sleeping under the stars.  Made from DWR treated Pertex Quantum and filled with 850+ loft Ultra Dry Down this sleeping bag represents the pinnacle of ultralight warmth and comfort.  It is one of the lightest sleeping bags I’ve ever seen with an astonishing warmth to weight ratio.

I tested this bag in my backyard during a 42° F night.  Crawling into it on my deck wearing a t-shirt and athletic shorts (after letting it loft for about 15 minutes) I instantly became warm and was more than comfortable.  I’m 5′ 7″ tall and this sleeping bag is big enough to roll around in or sleep on my side with a knee pulled up and never hit the side of the bag.  While there are not many features built into the SPI (its goal is to be lightweight) it does have sleeping pad retention loops down the sides and a collar cinch cord to adjust hood fit.  I really like the semi transparent material the Sea to Summit chose to use on this bag – for some reason able to see the down on the inside makes me happy.  The only mildly annoying thing about this bag is the very short side zipper.  While not really a problem you can’t unzip the side and stick a leg out to cool off if you are overheating.

Trade offs on the Spark SPI, like a short zipper, result in a sleeping bag that weighs next to nothing.  Mine weighs 12.39 oz on my home scale.  With a lower extreme limit of 23° F and its ability to compress down to a ball about the size of my fist I’m seriously considering including this bag in my backcountry ski kit as an emergency sleeping bag.  That is the beauty of an ultra lightweight sleeping bag – the potential uses grow when the main deterrents to packing it (weight and compressed size) become almost negligible.

Look how small it compresses!

Look how small it compresses!

Besides making a quality sleeping bag, Sea to Summit ships several documents along with it.  The first is an independently reviewed down quality rating from the IDFL.  The second is a letter discussing the benefits of Ultra Dry Down.  Honestly I don’t care too much about these documents but it was a nice inclusion driving home the point that you are receiving a quality product.  There was one line in the letter about Ultra Dry Down I did appreciate – “Sea to Summit does not use live plucked down.  We choose to source down from suppliers that have supply chain traceability audits preformed by the IDFL.”


The Sea to Summit Spark SPI is an amazing sleeping bag.  If you are looking for a lightweight sleeping bag you should buy this bag.  Its not even that expensive compared to other top of the line sleeping bags (MSRP $299 –  includes a compression sack, storage cube and laundry sack).

Sea to Summit Spark SPI Sleeping Bag

UPDATE #1: Its been several months now since I first picked up this sleeping bag and reviewed it. I’ve take it into the woods many times as well as to music festivals, couch surfing, and car camping.  In every scenario I can’t think of a better sleeping bag to have with me.  Because it compresses into such a small package I find myself using this bag far more than anticipated.  Heading to Uncle Jim’s house for Thanksgiving and not sure what the sleeping arrangements are? Toss it in along with your sleeping pad so you don’t need to worry about getting a good nights sleep.  I also had a chance to, unexpectedly, test how well the treated down works when I dumped an entire 20 oz. mug of coffee into the inside of my bag (whoops…).  Turns out it works great! I rinsed the sleeping bag out in a creek so the coffee wouldn’t stain or leave any sticky residue (which got the bag even more soaked) then hung the bag from a tree branch using the sleeping pad retention loops.  After about 4 hours it was dry and ready for action again.

UPDATE #2: I’ve also had a chance to test out the Sea to Summit Spark SPIII sleeping bag.  Check out the review!

2 thoughts on “Sea to Summit Spark SPI Sleeping Bag Review

  1. Anna

    Hey there! I’m looking at getting this bag, and I have just one question I was hoping you could answer. I read a review of this bag which the buyer mentioned that when they received it they noticed (unlike the advertised pictures) the logo was on the yellow side and the product contents tag was on the silver side, and they were confused about which side should they sleep in and which should be used as the outside for durability reasons. Did you notice this as well and/or do you believe a specific side of the bag should be used for the outside for durability? Thanks for the review! Hope to hear from you soon.

    1. Benjamin Bressler Benjamin Bressler

      I don’t remember off the top of my head where the logos are located but I can say that the white side is the outside and the yellow side is the inside. The sleeping pad retention loops, zipper placement and hood construction all reinforce this idea. Also, the yellow internal color makes it easy to spot a lost sock or other item floating around the inside of your sleeping bag. Finally, if you look at the fabrics used the white material is 10D Pertex Quantum treated with DWR (the water repellency makes it a perfect outer shell) while the yellow material is a soft touch, high density weave of 15D nylon (meaning its difficult for feathers to poke through and bother you while still retaining a soft feel for comfort against your skin).

      Hope this helps!