This decision is made by knowing the type of material you will be working with.
Open Coat – Here, the abrasive granules cover from 50% – 70% of the backing and are set at pre-determined spacing to reduce loading. Used on softer surface materials that tends to load or fill the abrasive surface.
Closed Coat – Here, the abrasive granules cover virtually the entire backing surface. Used where loading of abrasives is less of a problem.
What is a mesh vs. Grit size?
If you take a (1) inch space and add wires to it, the number of openings within the 1″ space is defined as mesh. For example, if the 1″ space has ten openings for particles to fall through,