What does a "C" or "D" backing indicate in sandpaper?

A "C" or "D" backing on sandpaper indicates heavy strength. This classification is associated with the durability and stiffness of the backing material used in the sandpaper. A heavy strength backing is designed for demanding sanding applications, providing support for aggressive sanding tasks and ensuring that the sandpaper can withstand greater pressure and wear without tearing or breaking. This makes it suitable for surfaces that require significant material removal, such as wood, metal, or rough finishes.

On the other hand, options like light strength and standard flexibility refer to different types of backing that are intended for lighter sanding or more delicate applications. Water resistance pertains to specific types of sandpaper designed for use in wet sanding, which is unrelated to the backing strength classification provided by "C" or "D."