The dreaded slow leak. I got a couple of Exped Synmats for us several years ago. We have well over 100 nights on them in the various deserts with their thorny plants and sharp little rocks. Finally on our last trip mine developed a slow leak, so slow it took four hours for my hip to start contacting the ground. I blew it back up and slept till morning but every night became a pain. No way could I find it out there.

When we got home I lay it out on a tarp and sprayed soapy water over it. That did the trick. There was one spot where a very, very slow bubble came up. I had to double the mat over and put extra pressure on it so the bubble would form. It was the most difficult leak ever to find, easy to patch though.