The z-rest pad has had the folding into the shape of a sit pad thing going for a number of years now. I like it in the rain, you only unfold enough for folks to sit on - fits naturally along a log for instance.
What I have done in the past is cut a few sections off a full sized z-rest pad to use as the sit section. I use the main pad for sleeping on and then the extra sections as a lumbar support section. Works wonders for those like me!
The z-rest also worked well as a seat cushion at the football stadium. We have some aluminum seat sections that suck the heat out of your tush when it gets cold late in the season. Folds up and is easy to carry back to the vehicle too!