We recommend using glass fiber prefilters for filtration of solutions with high viscosity or especially high particulate load. The glass fiber prefilters are available as an optional accessory and bundled with select Thermo Scientific Nalgene Rapid-Flow filter units. The prefilters enable a higher volume to be filtered before significant flow decay by trapping and preventing the larger particulate matter from entering the final filter membrane. Simply place one prefilter on top of the membrane bonded inside the unit, wet slightly to hold in place, and proceed with filtration as usual.