Abstract: An air filter comprising a first layer of reticulated foam plastic material having a thickness of between 10 mm and 20 mm and a porosity of between 5 and 60 pores to the linear inch, a second layer of reticulated foam plastic material having a thickness of between 6 mm and 10 mm and a porosity of between 60 and 100 pores to the linear inch, and at the interface between said first and second layers an open mesh substrate approximately one millimeter in thickness constricting a maximum of about ten percent of each of the first and second layers, the filter being impregnated with a flame proof retention and plasticizer additive, the first and second layers being bonded together at the interface.