In warmer weather I've taken to often using a folding backpacker's chair as pad and leaving other mats at home. The thing is maybe one-third again as heavy as the lightest-weight Thermarest inflatable pad, much bulkier, and no where near as comfortable for sleeping, but it does the job, and I really, really like the chair function.

I know there are kits that convert a Thermarest pad into a chair, but haven't tried them and am too cheap and lazy to bother. Also, am concerned that they might put lots of wear on pad, which continues to hold up well after 10-12 years of careful use.

I also have a really ratty old closed cell pad that, due to disintegration, has become much more compact and somewhat lighter than when it was new. I leave it in my car for those times when I forget to pack pad, or to supplement Thermarest in winter. If I'm super-concerned about weight and bulk, that's all I use.