NOVELTY - A high porosity polymer fiber sheet contains a three-dimensional matrix of polymer fibers, the matrix having thickness and interconnecting pores that communicate throughout the thickness of the matrix, and a fiber modifying agent distributed throughout the matrix, the fiber modifying agent anchored to the polymer fibers of the matrix and providing instantaneous and sustained wettability to the high porosity polymer fiber sheet. The fiber sheet is instantaneously wettable by an aqueous medium.    USE - A high porosity polymer fiber sheet for lead-acid batteries.    ADVANTAGE - The polymer fiber sheet exhibits high porosity and good tensile properties in both wet and dry states and maintains its wettability even after repeated washing and drying cycles. The fiber sheet can be densified and embossed to provide a desired thickness and porosity.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) high porosity multilayer composite polymer fiber sheet containing 1st high porosity polymer fiber sheet layer including 1st three-dimensional matrix of polymer fibers and 1st fiber modifying agent distributed throughout the 1st matrix, the 1st matrix thickness and interconnecting pores that communicate throughout the thickness of the 1st matrix, and the 1st fiber modifying agent anchored to the polymer fibers of the 1st matrix, 2nd high porosity polymer fiber sheet layer including 2nd three-dimensional matrix of polymer fibers and 2nd fiber modifying agent distributed throughout the 2nd matrix, the second matrix having thickness and interconnecting pores that communicate throughout the thickness of the 2nd matrix, and the 2nd fiber modifying agent anchored to the polymer fibers of the 2nd matrix, and the 1st and 2nd fiber modifying agents imparting to the respective 1st and 2nd polymer fiber sheet layers, and therefore to the multilayer composite polymer fiber sheet, instantaneous and sustained wettability by aqueous medium; and    (2) method of producing high porosity polymer fiber sheet that is instantaneously wettable by aqueous medium which involves processing mixture of polymer and fiber modifying agent to produce sheet of polymer fibers.    DESCRIPTION OF DRAWING(S) - The drawings show side-by-side photographs demonstrating the wetting behavior of densified polyethylene fiber sheets coated with surfactant and surface modifying agent.