A plurality of different layers of filter media are used to remove siloxanes from a gas stream. Based on an analysis of the specific gas stream to be filtered, a filter media having an average pore size enabling the preferential removal of a specific class of contaminants is selected for each different class of contaminants. The layers are arranged in sequential order such that contaminants having a higher molecular weight are preferentially removed by the first layers. Collectively, the layers define a segmented activity gradient that enables each class of contaminants present in the gas stream to be preferentially removed in a different layer, preventing removal competition between different classes of contaminants. A polymorphous graphite is used as the filter media, because that material is available in a range of well-controlled pore sizes, as opposed to conventional activated carbon filter media, which generally exhibits poorly-controlled pore sizes.