Electro-magnetic-energy absorbing materials are used to treat air filters, such as those used in association with electronic equipment thereby suppressing the transmission of electromagnetic interference (EMI) therethrough. Disclosed are processes and materials for applying EMI-absorbing materials to air filters thereby improving EMI-shielding effectiveness in an economically efficient manner. In one embodiment, an absorptive solution is prepared using an absorptive material and a binding agent. A heavy coating of absorbing solution applied to an air filter substrate, for example by dipping or spraying. Excess absorbing material is subsequently removed and the absorbing material cured, such that the passage of air through the filter remains substantially unimpeded. The resulting absorptive air filter is then optionally treated with a flame retardant to meet a predetermined safety standard.