@Nine hey, they're chrome tapes, so they're not bottom-of-the-line ones! (there were four different formulations; type 1 or ferric was the cheapest, then type 2 or chrome was better quality, type 3 or ferro-chrome was not really much better than type 2 and was pretty short-lived, and then type 4 or metal was most expensive and highest quality)
@Nine @BatElite The metal tapes use actual metal powder or foil; I'm not sure what specifically but I would assume some type of iron alloy, possibly with some cobalt added
they'd want to prevent rust, but it won't be normal stainless steel because that has poor magnetic properties (you may have noticed that magnets don't stick to stainless steel silverware)