2 or 6 pack of professional PM 2.5 Activated Carbon Filter replacement pads that fit prfectly in our Adult and Child size covers. These filter pads filter fine dust and particles. It has 2 layers of non-woven fabric, 2 layers of of filter cotton and 1 layer of activated carbon cloth. Theses filters are disposable and the recommended use is 3-5 days. Approximately 4.7"x3.1"