Sartoguard NF prefilters feature a combination of polyethersulfone membranes and nanofleece technology. The nanofleece technology provides an ultrafine fleece structure based on a small nanofiber diameter of 120–150 nm. The resulting fleece structure offers clarification capabilities even for extremely fine contaminants along with a high-dirt holding capacity and high total throughput performance. Sartoguard NF prefilters work well for downstream protection of sterilizing-grade and mycoplasma-retentive filters in prefiltration applications for biopharmaceutical manufacturing.