I believe the R-value is the same for both. The 9 is both wider & longer so you're not as likely to roll off it if you thrash around a bit at night like I do. I use the 7 because it packs smaller. I found after changing from the Big Agnes--which slipped & slid all over--that I didn't roll off of the Exped. If you are a bigger guy, you might want to go for the 9 just to make sure you are fully on the mattress. Pack size isn't that much different but I have a space problem (sportbike) so I go with the 7.