don't use devetyne. the flame retardant fibers come off in the form of dust that you don't want to breath or have to clean up. also look up "ultrabounce" at modern studio equipment. it's like white/black ripstop but opaque. black out "paper" is also used in the film industry to seal up windows/doors. if you're basement isn't too bright you may get away with plain old black ripstop nylon which is available at any fabric shop.