I'm not too keen on the use of multiple layers of foil, since, when heating food like soup or pasta, it is very likely that food residue will become trapped between the layers. I don't like the use of staples, either, for similar reasons.
I'd suggest that a better material is the unrolled side wall of aluminium drinks cans, which is thick enough to make a reasonably stiff lid, whilst still being very light. A very small folded lip, or shallow folds across the lid can add further stiffness if needed. Also recycled.