What they said, LOL!  Just to clarify, if the tank has a bottom internal brace, then you still need the foam.  If its an external brace (like the ones you see on regular tanks) then you don't need it.  For examble, I think the deep blue tanks are have a plastic brace, so no foam needed.  Reef Savvy recommends 3/4" foam, but I've heard of people using less.  I got mine at home depot, like $10 for an 8 x 4 sheet!