I recently bought one of these to provide a little extra warmth for a camping trip as I get cold at night quite easily. For £20 I didn't actually expect all that much but it has turned out an excellent purchase. The liner packs very small and is very light so doesn't take up room or weigh you down and as it does actually make a big difference it allows you to have an "adjustable" sleeping bag and could also be used on it's own during summer. At the time of purchase, I was tipped to try it both on the outside and inside of the sleeping bag as depending on your size and what you wear in bed it might work better on the outside (the outside of the liner is shiny and the inside more fleecy) but having started the "trial" with the liner on the inside of the sleeping bag I ended up sticking with it as it was very comfortable and there were no issues with the liner wrapping around you in the bag as can happen with cotton liners, etc. The bag is a generous size and although it has no zip (less weight and pack size!) I found it very easy to get in and out of even in the dark, in a small tent. All in all a great buy and a very cheapand convenient way to be As Snug As a Bug In a Rug.