I have referred a mask used for ventilators and changed the inlet, allowing replacement cotton/paper/tissue filters to be fitted using the Cap to secure filter sheets around the periphery of the Mask extension. Filters are placed between the main body and the cap. Clearance between inner diameter of Cap and outer diameter of mask protrusion is 2.5 mm, allowing multiple sheets of kitchen towel, fine cloth, dense filter sheets etc. to be fitted.

As with all filters, they need changing regularly (every 2 to 4 hours). Wear gloves when changing filters. Disinfect/Steam Face Mask and Cap each time when changing filters.

Large intake cap allows larger filter surface area/volume and denser materials. It is important to reduce air flow by introducing larger surface area/volume/density of filter. You do not want small diameter filters as this concentrates collection of moisture, germs and virus, reducing efficiency of filter. Smaller intake sizes also requires more porous filter materials to be used making the filter vulnerable and reduced replacement time.