Ok, here are the different methods of insulation:

Cork board (sold for pinup boards usually) Works well for my corn snake tanks since they don't need as much heat as BPs:

And a closeup of one side:


Foam board (home insulation material) The preferred material for BP tanks:


And, just to show what it looks like, the felt insulation I use on my tubs: (self-stick felt)


Hope that helps.