Here is a fairly good article on the subjecct.
"Radiant barrier spray-on paint is essentially liquid foil. While not all radiant barrier paints are the same, basically they are made by grinding pure ... read more
Painting over thermo foil will not be a long term solution. It is a smooth non-porus material. Your best bet is to replace the doors. There are lots of options today that weren't available a few years ... read more