Because they are reliable,light and easy to carry.
A transparent ruler may be a polycarbonate. An opaque-type ruler may be a polystyrene copolymer such as high-impact polystyrene (HIPS). Recycled polystyrene can be turned into rulers, among other...
Nylon
man made plastic is made from petruelum
by hydrocarbons glued together i think but not sure