When people talk about "rubber", they don't usually specify
what kind. There are many different kinds of rubber, but they all
fall into two broad types: natural rubber (latex—grown from plants)
and synthetic rubber (made artificially in a chemical plant or
laboratory). Commercially, the most important synthetic rubbers are
styrene butadiene (SBR), polyacrylics, and polyvinyl acetate (PVA);
other kinds include polyvinyl chloride (PVC), polychloroprene
(better known as neoprene), and various types of polyurethane.
Although natural rubber and synthetic rubbers are similar in some
ways, they're made by entirely different processes and chemically
Natural rubber is made from a runny, milky white liquid called
latex that oozes from certain plants when you cut into them.
(Common dandelions, for example, produce latex; if you snap off
their stems, you can see the latex dripping out from them. In
theory, there's no reason why we couldn't make rubber by growing
dandelions, though we'd need an awful lot of them.) Although there
are something like 200 plants in the world that produce latex, over
99 percent of the world's natural rubber is made from the latex
that comes from a tree species called Hevea brasiliensis, widely
known as the rubber tree.