The metal foil covering of some wine bottle tops is sometimes made from some silver-grey malleable metal - I know it’s not aluminium, as it’s too soft. Is it tin?
At one time, wine capsules were made of tin-coated lead foil. That was banned by the FDA in 1993, although it’s not clear how much hazard it really presented. Since then, wine manufacturers, at least US domestic ones, have experimented with various forms of tin, aluminum and plastic foils. According to this article, tin gained in popularity in 2006:
yabob answered your question perfectly.
Tin is the metal used for many capsules. There are less expensive options though, such as PVC and polylam and proprietary blends such as Maverick’s AT (Almost Tin), as noted in the article linked.