Whatman 1442-042 Quantitative Filter Paper Circles, 2.5 Micron, Grade 42, 42.5mm Diameter (Pack of 100) Diameter: 4.25cm Retention: 2.5m A world standard for critical gravimetric analysis with the finest particle retention of all Whatman cellulose filter papers A Whatman cellulose filter is manufactured from high quality cotton linters treated to achieve a minimum alpha cellulose content of 98% Typical analytical precipitates include barium sulphate, metastannic acid and finely precipitated calcium carbonate