if you go with polycarbonate or any other rigid material we have used up to 10mil thick after that you have issues with head strikes and even the 10 mil sometimes not so good. make sure you have your longer clip/guides on the machine also roll out some slack so it doesn't have too much tension on the machine then it will buckle sometimes.
never saw a clear banner material, new one to me closest to something like that i would think would be clear static cling