In our class (that I have to take every single year) shows a chart of common materials in a manufacturing environment. Some are VERY capable of generating ESD, while others are not. The chart showed that if you took 2 pieces of styrofoam, rubbed them together, instant ESD. 2 pieces of wool, instant ESD. 2 pieces of glass, nothing, 2 pieces of wood, very little, if any at all.