That distinction will depend upon what brand(s) you are considering, though I have not heard of any ill effects with the great stuff foam sealant. Great stuff on the other hand is more of a spray foam, so it will be a little harder to work with, though you can spray it directly to a piece of coco-mat and the transfer it. On second thought, it might be easier just to use coco-mat. Some products like hermit crab climbing backgrounds (found at PetsMart, Petco) are feasible, though you might need to cut a few pieces to size the dimensions of your dividered, then glue them together (aquarium sealant would work fine). Give a little more info on the exact nature of this divider and what the situation with the tank is already and I'll be able to be a little more specific myself. Best of luck
Jeff
1.0.1 Ventrimaculatus
0.0.1 Azureus