What is the difference between TO-220F and TO-220FP cases?
The STP12PF06 datasheet (first google hit for 'to-220p to-220fp') shows that the f version has a metal tab, and the fp version has only plastic on the outside (at least at the front, but I assume also on the back).



This makes it easier to mount the package galvanically isolated, but the plastic layer seems to add some thermal resistance: the rthj-case of the fp version is almost 3 C/W higher.