I saw them demonstrating one after some crash a few years ago and it was a wire recorder. It really surprised me because in the late 50’s, early 60’s my dad had a wire recorder and I was amazed that it could record stuff.
For an aviation black box it is perfect because of its durability to the elements, water, etc and can be recorded over almost indefinitely, unlike tape. As well, a whole lot of recording time can be stored in a small package.
Now, the foil recorder you are talking about.......did it come over on the Santa Maria? LOL, LOL.
Ha ha ha, those foil FDRs were a PITA. The foil was razor sharp.