I made this filter to remove the toxic volatile organic compounds and fine particles generated by my 3D printer. It is about 11x11x20 cm big, and contains a HEPA 13 filter and active carbon pellets. There is a door on the exhaust pipe to redirect some of the air back into the enclosure, to keep a correct temperature inside. It is difficult to test its efficiency without proper tools; at least, the smell when I open the enclosure is much lighter now that I use this filter...