I just assumed they were resin as there were tons of them, i'd imagine it'd be easier to make one and cast multiples from the mould, rather than hand make each one? but then i don't know anything about leather really
Well, I can tell you what definitely DOESN'T work: Molding the leather over your own eye.
Watched again, it looks like the screen used eye patches are white on the back and gloss black on the front. You can see the layers from the side, especially on River's since hers is so poorly fitted. So maybe not leather at all. What else forms? Styrene? Maybe they're vac-formed then painted with something like black plasti-dip?
Id say either vacume formed OR maybe even Latex. They would have to be light weight to be able to stick well on the actors' faces.
I was also thinking about doing this - and maybe even the Doctor's store ID badge "The Doctor - I'm here to help" haha
Just a small update, I'm pretty sure it's formed styrene sheet with black garment leather glued to the front. If I can get my hands on the one part of the Rory costume that's proving tricky to get, I'll definitely be making myself one of these.