K-36 is a catalyzed primer surfacer. it is fuel proof upon curing, and sands wonderfully filling very minor imperfections. the sanding is the real beauty of the product imho. K-36 seems to be a very stable "substrate" for paints as well. I have not come across anything that did not "stick" well to it.

FWIW I have tried the "low-iso" version (ncp 250) which is a purple-ish gray color. I believe the K-36 still sanded better, and the purple-ish gray color was a bit strange to "see" how smooth my "fill" work was.