Abstract: Disclosed herein is an electromagnetic radiation absorber comprising a filamentary, three-dimensional, porous substrate of dielectric material having a relatively thin layer of electrically conductive material deposited thereupon. The layer is characterized by a generally gradual and continuous reduction in its thickness or bulk with inward progression into the substrate from one side thereof, thus resulting in a layer exhibiting a graduated resistivity. A filler substantially pervious to the radiation of interest may be disposed in the interstitial voids between filaments, and relatively small diameter magnetic/magnetizeable particles may be suspended in the filler to thereby further extend the useful frequency range of the absorber. Also disclosed is a sputtering method for producing such an absorber.