Reviewed by Jason - 12th Aug, 2018 Amazing but flawed.... Amazing comfort for such a small item, I'd never go without now. Foam is dead to me. This little thing fits happily in a cage cable tied to the fork leg on my mountain bike. The bag it lives in is theoretically waterproof. The reason I say it's flawed is that my first one started to deflate during the night after a few months of having it (admittedly I did use it a lot....) so I returned it &..... The replacement has recently started doing the same! I cannot find a leak anywhere to use the included patch kit on however! (It must be tiny). I once had to wait 3.5 hours at Castle Cary train station in sub zero temps at night. Rolled this thing out on a bench & the amount of warmth it traps & returns into your back is amazing. I was like some kind of fancy homeless dude feeling sorry for the wealthy commuters freezing their asses off in their work attire.