Prefilters are often prepared from depth-type media, a random matrix of material which may or may not contain binder. These filters trap particles within the matrix and therefore have a high loading capacity. But because of this design, these filters do not have a clearly defined pore size, only a nominal rating. These filters have applications outside of prefiltration, such as air and water pollution analysis, liquid clarification, and cell harvesting.    

If used as a prefilter, the filter should have a slightly smaller diameter than the filter membrane it precedes: Filter Holder Model (Vacuum Type) Recommended Prefilter Diameter (mm) If preceding final filter If used as final filter 25mm models KG 25, KGS 25 16 25 47mm models KG 47, KGS 47, KSF 47, KGS 47 TF 35 47 90mm models KG 90, KGS 90 70 90   Filter Holder Model (Positive Pressure Type) Recommended Prefilter Diameter (mm) If preceding final filter If used as final filter 13mm models KS 13 8 13 25mm models KS 25, LS 25, LP 25, KS 25F, PP 25 21 25 47mm models KS 47, KST 47, KS 47F, LS 47HP 35 47 PP 47, PFA 47 42 47

Prefilters made of dense borosilicate glass fibers:
	Biologically inert with high chemical and thermal resistance
	Unaffected by humidity and can be stored indefinitely
	Can be easily sterilized by autoclave or baking
Product Specifications*
Type     Applications/Comments Weight (g/m2) Thickness (mm) Nominal Rating (μm) Binder Max.Temp.(°C) GA-55 General purpose paper; suitable for air pollution monitoring 55 0.21 0.6 None 500 GF-75 Most retentive grade; suitable for collection of IgC or other very fine protein precipitates; use to clarify aggressive chemical solutions; suitable for TCLP (EPA Method 1311) when used with KST142. 75 0.35 0.3 None 500 GA-100 General purpose paper; suitable for filtration of precipitated cells or proteins, and air pollution monitoring 110 0.44 1.0 None 500 GA-200 Thick paper; suitable for filtering viscous fluids such as liquid sugars and gels 175 0.74 0.8 None 500 GB-100R Has low trace metal content; suitable for DNA?RNA and protein precipitates 95 0.40 0.6 None 500 GB-140 Thick with moderate wet strength and loading capacity; suitable for industrial waste analysis 140 0.56 0.4 None 500 GC-50 For use with 0.45μm or smaller membrane filter; suitable for scintillation counting and filtration of suspensions in industrial and waste water 48 0.19 0.5 None 500 GC-90 High wet strength; suitable for clinical screening 100 0.30 0.5 Organic 120 GD-120 High wet strength and high loading capacity 123 0.51 0.9 None 500 GS-25 High wet strength with moderate loading capacity 70 0.22 0.6 Organic 120 DP-70 High wet strength and loading capacity; suitable for dust mearurement 170 0.52 0.6 Organic 120