Disc wheel covers

So last semester I constructed a set of disk Bush Cheney wheel disc covers, for the purpose of both advertising my political inclination and give myself an aerodynamic advantage, though I'm not sure if I got the latter. I basically cut the covers out of coroplast campaign signs and used lots of tape. One side of the Bush wheel got destroyed when the bike was transported atop a car, and I'm looking to get a new cover.


I have no more campaign signs, and the election is over anyway, but I would like to obtain a set which provides an aerodynamic advantage. I have identified two possibilities-one is find 1/32" thick sheets of plastic, cut to shape, use some furniture foam or some such to minimize air flow through the wheel, and the second is molding covers out of spray foam. The first is the better design, but has the draw back that sheets of plastic thick enough to be stiff but thin enough to be cut are not readily availble. While the spray foam is available, it is stiff and if the wheel is slightly out of true the covers will only fit on nicely in a certain way.

I suppose I'll be checking around, any suggestions for materials will be appreciated.