Sea to Summit Spark SPIII

Sea to Summit Spark SPIII Sleeping Bag Review

Sea to Summit has followed up their release of the Spark SPI sleeping bag with the release of two, warmer, versions – the Spark SPII and Spark SPIII.  I recently began using the SPIII to see if I liked it as much as I did the Sea to Summit Spark SPI.  Its essentially the same bag just with more down to make it warmer.  Its still the lightest in class bag for the 25 degree (F) range coming in on my home scale at 21.1 oz. (just as the SPI is the lightest in class 46 degree bag), it’s made with the same treated Ultra Dry Down and Pertex Quantum shell to get it as waterproof as possible and it still packs down ridiculously small.  Check out my review of the SPI to get a full understanding of this sleeping bag.  From here on out I’m going to talk about the small differences between the SPI and the SPIII.

I recently took the SPIII on a snow camping trip and overall it worked well.  The bag is so light that you will most likely drop at least a pound by switching to it – this is huge. This fact alone almost makes it an easy decision to switch.  But, when I used this sleeping bag I noticed the trade offs I discussed in the review I wrote of the SPI more in the SPIII than in the lighter weight version – specifically the short zipper which helps make the bag so light.  When I’m all bundled up and crawling into the sleeping bag the extra hassles of winter camping make the short zipper a little more irritating.

Sea to Summit Spark SPIII in use

You can see the Spark SPIII on the right. I’m also using a Big Agnes Fly Creek UL3 tent, Big Agnes Q-Core SL sleeping pad and Sea to Summit Aeros Ultralight pillow.

This bag also doesn’t quite seem to hold up to its 25 degree (F) temperature rating.  During my test I slept on top of snow in a three season tent set up on a fairly protected campsite using the Big Agnes Q-Core SL sleeping pad (its has an r-value of 4.5), wearing the OR Halogen Hoody, a long sleeve shirt, hiking pants and medium weight socks.  The nighttime temperature was somewhere in the high 30’s or low 40’s (F) and I woke up a few times feeling slightly cold.  Sure I could have put on another layer and have been fine but I’ve used other sleeping bags rated at the same temperature rating during similar conditions and slept in just a t-shirt, shorts and light socks and been perfectly warm.


The Sea to Summit Spark SPIII is an awesome sleeping bag that is so light most people shouldn’t hesitate to switch to it.  The majority of people who backpack do so during more mild temperatures and won’t need to worry about pushing the lower limits of their sleeping bag.  When I go into the backcountry during cold temperatures I always bring a full set of down with me to wear once I’m in camp – check out my packing lists to see exactly which pieces I like.  Because of this I can get this bag to work in the temperature ranges I need it to by wearing my down inside my sleeping bag, maximizing my warmth to weight ratio by layering my sleep system just like you layer your clothing. But if you want to sleep in just your skivvies during the colder nights you might want to find a sleeping bag that is truer to its temperature rating than the Sea to Summit Spark SPIII.

Sea to Summit Spark SPIII