Whatman 1441-110 Quantitative Filter Paper Circles, 20 Micron, Grade 41, 110mm Diameter (Pack of 100) Diameter: 11.0cm Retention: 20m Fastest ashless filter paper Recommended for analytical procedures involving coarse particles or gelatinous precipitates (iron or aluminium hydroxides) Used in quantitative air pollution analysis as a paper tape for impregnation when determining gaseous compounds at high flow rates