i use foam core and cardboard circles in ten thousand variations 
sometimes cardboard circles need some oomph if one is not enough
and you can put two together criss crossed for strength
sometimes you might wanna run bamboo skewers through the corrugations for strength
maybe criss cross that too depending on how you're using them
i often hot glue those together if using more than one
all depending on the weight and moisture content etc
those cardboard circles can get sotted with moisture and grease so for larger tiers i might use the foam core
some cardboard circles are waxed but usually just on one side
and the foam core needs to be cleaned i think
Rae of BlakeCakes cleans her foam core with vanilla* and then waxes them with food approved soy wax for safety which i think is brilliant
*pretty sure she said vanilla--an alcohol based substance that dries quick
i'll go check--don't wanna misquote
