Robert Hwrote a review of Sea To Summit Spark SpIII Sleeping Bag: 25 Degree Down on August 7, 2017
Familiarity: I've used it several times
This bag is my new favorite piece of gear! It is incredibly light weight, packs down TINY, and is incredibly comfortable.
Being about 6 ft 2, I went for the long option... That being said, I'm confident I would have comfortably fit in the regular size... There is loads of space for me in the long when I am stretched out all the way... Enough space for extra clothing/snowboard boot liners.
Included with the bag is a compression stuff sack which is extremely effective. The long bag takes a little effort to stuff into the bag, but once stuffed the compression straps synch it down until it cannot be synched no more. You are left with an incredibly dense bag that fits inside of a mesh trucker hat. I have so much space in my pack now compared with my old bag that I"m considering getting a smaller pack... I just don't know what to do with all the extra room!
The 1/2 length zipper was a concern of mine after reading a few other reviews. It turns out it is not a hassle at all. I'm no super flexible yogi, and at my height there is no fumbling to get in or out of the bag at all.
I have only been using it in summer time, and it is quite warm. I have not tested the low end of the temperature spectrum, but I am quite excited for some late fall/early winter backpacking now. The bag is almost too warm for camping out in the summer heat- consider the SPI or SPII if you are looking for an even smaller, lighter bag.
The only negative that I can think of is that the foot box is a little bit tight. My former bag was a Big Agnes, which had excessive amounts of room to spread your legs and bend your feet. The SPIII limits me to spreading my feet just narrower than shoulder width due to the taper of the slim fit. It is not claustrophobic, however- just slightly restricting. Worth it for the packability in my opinion!
The biggest problem is the thing is so damn comfortable, I have a hard time getting out of it in the morning! I am sincerely looking forward to some cold weather camping in this sucker! It is small enough and light enough that I would consider taking it on long day ski tours as an extra safety buffers should I get stranded. (I'm willing to bet that this bag compresses smaller than most 650 fill down puffy coats and bulky synthetic coats!