Made of borosilicate glass LBG 3.3. They should be used with a filtering flask with standard ground mouth reference FFK3. Each funnel has a sintered disc with a different porosity grade: 90-150 ?m (porosity 1), 40-90 ?m (porosity 2), 15-40 ?m (porosity 3), 5-15 ?m (porosity 4)