I think all tubes,irrespective of vehicle are made out of BUTYL rubber nowdays.

At least the ones I've seen have been,its been written on the sides.

I have seen pictures of butyl stretched to unimanagable extremes from bomb blasts etc over 30 years ago when it was first introduced to the UK..It was actually a single membrane ,bespoke sheet applied to flat roofs and reservoirs/ponds/lakes and water tanks.