That's exactly correct! The CAT itself is some kind of super metal foil that can take extreme heat without disintegrating and is built very similar to cardboard except in a circular fashion so as to end up a cylinder shape. The problem with drilling is that a drill bit has to be able to bite and pull itself into the material which it can't do in this case because the very thin foil simply folds over at the contact point and the bit just rubs and doesn't cut. Almost as if it's gummy?
I think you have to gnaw on it with a hole saw first to get it pierced and then, with long needle nose pliers or chisels, start peeling away the layers from the center, so as to make the hole larger and larger until you remove it all. It's by far the most time consuming part of the process. Slitting the can open from the back as I did and welding it back together didn't take any time at all.
