An ultra-efficient multilobal cross-sectioned fiber filter for chemical contaminant filtering applications is described. An absorptive chemically reactive reagent, preferably an acid or base and in liquid or an adsorptive chemically reactive reagent (an acid or base) in solid form, is disposed within longitudinal slots in each length of fiber. The reagent may be used alone or in conjunction with solid adsorptive particles which may also be utilized with the reagents in the longitudinal slots within the fibers. Reagents within the fibers remain exposed to a base-contaminated airstream passing through the filter. Base contaminants in the airstream, chemicals such as ammonium and amines (as well as particles), react with the acid reagent within the longitudinal slots of the fibers. As the contaminant and reagent react, the ammonium or amine becomes irreversibly absorbed (or adsorbed if reagent is a solid acid) to the liquid acid reagent and multilobal fiber.