An old friend from frog was doing these a couple years ago… USB Sticks encased in concrete
There’s a similar technology called ‘potting’ electronics - which is surrounding a board with caulk or nonconductive grease so when an it goes under water (and under pressure), the enclosure won’t let water in.
I’d imagine that USB sticks would have a pretty heavy layer of mask on the circuit board to protect it, since it might go in washing machines, etc. Mask is the spray-on clearcoat layer that goes on top of the pcb once it’s created.
That’d protect it from the whatever you coat it in, but the mechanical connections might not hold up when you stick it in again and again…