Not only does this styro-foam cornicework expand and contract but it is a fire hazard!.....Think what styro-foam does when it ignites......little drips of flame whizzing to the floor!
If anyone wants an embelished cornice or moulding they really should stay with what is known to work, not what is cost effective! If you don't, you'll spend 10 cents today buying it and installing it and then you spend 100 dollars tomorrow fixing it!
Stay with hand-carved wood (the laser carved wood looks just looks too phony) or use plaster.
If you want the look of the real thing but are looking for a replacement material for both wood and plaster then I would suggest using compo. Composition ornament is flexible when installed (just takes a little heat to make it fit the curves of the background of the cornice), it is self-adhering and it dries very hard. It's easy to paint and ages very well.
However......compo will cost quite a bit.
There are people out there who are looking for better alternatives to plaster (and wood) for the decoration in homes and buildings.....this styro-foam junk is NOT one of them.
As for the stuff that comes in a roll.......Why?
I mean, how can this stuff even resemble the real thing? I have never seen this stuff......but I still can't picture how it could ever have the depth or undercut of the hand-carved wood or molded plaster!
With this rolled stuff......I wouldn't do it......if you do use it.....be prepared to be a laughing stock when someone that knows what they're looking at sees it!