I realized that my vacuum cleaner does not have a HEPA air filter, and I was wondering if I could just put a few layers of tissue paper to filter the air. I looked at the surface of the existing filter and tissue paper with a 120x magnifying microscope, and the tissue paper seems to have a denser surface/less gaps than the original vacuum cleaner filter. Is that a good idea? Will it actually filter air? Will it ruin my vacuum cleaner?
tissue paper can be used as a filter for particulates in air, but because the material itself is so weak, a strong flow of air through it will cause it to tear to pieces.
In addition, even if it were mechanically strong, the particles it filters out would sit right on its surface, pile up there, and quickly plug up the pores in it and stop the flow of air through it.
For these reasons, air filters are often made with some metal mesh structure embedded in them to furnish mechanical strength and with a filter material that traps particulates within its thickness and not on its surface. This "thick" filter lets the filter last longer and trap a larger quantity of particles before it gets plugged up.