Millex Syringe Filter, Hydrophilic PTFE, HPF, Non-sterile: Background Information: Overview of Non-Sterile Millex® HPF Syringe Filters • HPF Millex includes two different media: a graduated glass fiber prefilter (10.0 to 0.7 µm) to remove larger particles and an 0.20 or 0.45 µm membrane filter for fine filtration