Grade 2: 8 µm Slightly more retentive than Grade 1 with a corresponding increase in filtration time (i.e. slightly slower filtration speed). More absorbent than Grade 1. In addition to general filtration in the 8 µm particle size range, the extra absorbency is utilized, for example, to hold soil nutrient in plant growth trials. Also used for monitoring specific contaminants in the atmosphere and in soil testing.