Both me and my friend have an OS-2, both same label and made in taiwan; (that is the only version); yet both the under rubbery material and the black bit your foot stomps on saying BOSS on the top are both different materials.
Mine is a really rough, rubbery texture, and the one on his is liek a hard plastic almost. Any explanations?
The rubber can age in different ways depending on the environment they are stored/used in. Spilling alcohol on the rubber could make it harder/brittler. I think Boss has pretty much stuck to the same material throughout the compact pedals life.
I'll have to chime in aswell and note that at least one of my pedals (I can't remember which one right now) is definitely made of a more plastic-like material than the traditional rubber material I expect out of Boss pedals. Not that this is bad by any means, I'm pretty sure it was an older pedal and the rubber probably would have aged a little more, but it still holds its shape perfectly.
I'll see if I can remember which pedal it is, dig it out of the bin and maybe take photos.