Filter Paper Grade 2. Circles: 42.5 mm to 500 mm (available prepleated) Sheets: 460 x 570 mm to 580 x 680 mm. Particle retention 1: 8µm. Nominal thickness: 190 µm. Nominal basis weight: 97 g/m 2. Nominal ash content 2: 0.06%. Grade 2 is slightly more retentive than Grade 1, with an equivalent increase in filtration