Thanks, now that you mention it I do recall having been told that Butyrate is the shrinkier dope... although I also know that nitrate will shrink more with a hotter thinner (i.e. if mixed with something liek acetone as compared to something like MEK or lacquer thinner).

BTW, I use micafilm, so I have experienced Balsarite but I have not experienced it coming loose in the sun. (Granted, I live in a relatively cool climate, but I've also had my sailplanes in the car for days at a time, so they would have experienced heat well in excess of 100 or 110 degrees there repeatedly and for several hours at a shot, but the covering never came loose.)