The Sea to Summit Reactor Thermolite® sleeping bag liner is a very nice light weight compact addition to your gear that will provide up to an additional 15 degrees F / 8 degrees C of warmth to any sleeping bag. It weighs 8.7 oz and packs down into a 3” x 5” sil nylon stuff sack. It shaped to fit into mummy sleeping bags however it will work for any sleeping bags or even quilts.
I have had several chances to use this and I honestly did not think it would work as well as it did. I had several people tell me that I should take a look at them and they were indeed correct stating that I would not regret the purchase. On one specific occasion I woke up in the middle of the night freezing and thankfully I had brought the line with me and was able to slip it in and get into it without having to get out of my mummy bag. Very shortly after I was situated I began to warm up and fell back to sleep.
Sea to Summit has several different liners for various types of activities and warmth. Check out their whole line here.
Do you currently have one of these in your gear stash? What did you like or dislike about the liners?