Grade GF/C: Combines fine particle retention with good flow rate. The standard filter in many parts of the world for the collection of suspended solids in potable water and natural and industrial wastes. Properties: Medium to fast, high loading. Particle retention in liquid (µm): 1.2. Particle retention rating at 98 percent efficiency. Filtration speed herzberg (s): 100. Basis weight(g/m sq): 53.