This is a plastic question about commodity hardware. Logitech mice and many other popular peripherals have an sprayed on or molded overcoat. It's a plastic of sort that turns into glue and comes off leaving shiny spots. Tends to fail entirely within 5 years, with the first sign of failure being around 2 years in.
In this video they call a "sticky rubber coating" so I'll go with that. It feels great when you buy it, and it's a great example of designed to fail. What is this horrible substance called?