This is a DIY particle filter with standard 40 mm thread, suitable for many half and full-face masks.

WARNING:

• only use when no certified commercial product is available due to e.g. supply shortages during a crisis and when you are very desparate!
• absolutely do not use when there are cracks, layer-separation or any other defects present in the print!
• drop each part from 2m / 6ft height onto a hard surface: if it breaks or cracks don't use it!
• use the filter until breathing gets more difficult, do not use it longer than 1 day!
• if you are using it as protection from things like saw-dust you can very carefully extract the filter material without releasing any dust, throw it away, wash and dry the filter and refill with new filter material BUT if you are using it as protection from biohazards and very toxic substances treat the whole filter as hazardous and dispose of accordingly!
• I absolutely cannot and will not garantee that this filter works at all nor can I guarantee that it isn't dangerous!!

Instructions:

• print casing, inner grid, outer grid and stencil using ABS for stability
• drop each part from 2m / 6ft height onto a hard surface: if it breaks or cracks don't use it!
• push inner filter grid into casing with the circular protuberance of the grid facing towards the threaded side of the filter (according to schematic)
• use stencil to draw 114 mm / 4.49" diameter circles onto microfiber dust wipes or microfiber vacuum cleaner bags, cut out at least 6 microfiber circles, stack them and place the stack into the filter according to schematic (there should be absolutely no gap between casing and microfiber circles!)
• tightly push outer filter grid into casing with the little knobs facing inside the filter (see schematic)
• test if you can easily breath through the filter: if not don't use!