Air humidifiers can help keep impurities out of the air and keep moisture in the air. However, the filters for air humidifiers can be rather expensive. Making a filter for an air humidifier can be a cost effective alternative.
Flatten 18 coffee filters, turning every other filter upside down.
Separate the filters into three stacks of six each. Cut every third ridge of the filters in each stack. Cut these ridges from the center of the filter. Discard the center of the filter.
Stack five coffee filters into each other and staple together. Staple the fins created from the other filters in the ridges of the five stacked coffee filters.
Place the filter in the humidifier and place the cap with coins in the center of the filter to hold it in place.
Change the filter whenever necessary.