I have egg crate in my refugium as well, but always bits of chaeto go through and end up collected at power head or irritating some corals. With a finer mesh, I hope chaeto will stay contained. Worried little bit about the flow.
I believe its Polystyrene, PET is used as a raw material as well as Glycol,TDI,Ethyl,styrene, Styrene as a liquid and by it's self is a known Carsen-generatic Once binded in to the process is perfectly safe as a plastic.