BS”D
You can put a chador on over a shell and a burqa on over just about anything and it will be kosher. If you follow this minhag, tin foil or orange plastic is most recommended for your chador or burqa. As is well known said tin foil or plastic should not come from a tzioinish source.
Mekor: “Extreme Tznius for Real Dummies” by Rebbetzin Izevel Tzoiah Yachne Schmoigerman