Sea to Summit Reactor

Summary

This thing will add warmth and extend the life of your sleeping bag.

This thing always goes with me, no matter which sleeping bag I'm using, because it adds the extra warmth or helps regulate my sleeping comfort temperature. It also does a great job in keeping my body odor or oils from getting on to a very expensive bag and thus extending the life of your sleeping bags.

This thing is awesome! I use it as a liner in all my sleeping bags to keep the clammy nylon feel off of my skin. It also lets you sleep most of the night with the bag unzipped if the nights are unexpectedly hot. 

Great product. I highly recommend it.

Picked one of these up from REI. Nice little liner.

Pros:
- Comes with compact, silicone-lined stuff sack.
- Has draw strings on the entry end that allow you to really block-out the cold
- Says "mummy" style, and it is, but it is a wide mummy on the foot end, allowing some movement. This could be a pro or con depending on how you view it. It was a pro for me because I have a rectangular bag - this liner allows some freedom of movement in the foot area.
- Very warm
- Fairly long. I am 6' and was able to comfortably draw string the end around my neck (all the way into a mummy-style breathing hole around my head if I was willing to sacrifice some foot movement room)

Cons:
- Stuff sack could have been about 3/4 its size

One more thing: don't add this liner to your bag on warm nights! I woke up sweating the first time I tried this thing. It works...

This thing is great and unbelievably warm for the size and weight... I carry it in the late fall and early spring to extend my 20 degree bag's range. On nights when I don't need the extra warmth I roll this liner into a fluffed up ball and tie it inside a bandana to make *THE MOST COMFORTABLE* backpacking pillow in the world. In the summer it makes a great lightweight quilt, and it can be used while traveling in hostels too.

pros: tiny, light, and warm...

cons: a bit pricey, and feels somewhat fragile (though it hasn't ripped yet).