Question:  What materials are the biggest cause ESD damage?

Answer:  Plastics and other synthetic materials cause the most trouble because they are insulators and trap charges on their surfaces.

Materials that are insulators hold an electric charge and cannot easily transfer the charge and cannot be grounded to earth by common means.  Conductors are just the opposite.  They are materials that easily transfer a charge.  Examples are metals, water, carbon and people. Understanding insulators and conductors is an important part of creating an ESD action plan.