A filter for blood and the like including a housing defining an inlet for fluids to be filtered, and an outlet for filtered fluid, plus a stack of filter pads of thermoplastic fibers positioned within the housing. According to one aspect of this invention, the stack of pads is joined together at their periphery by a heat seal to form an integral filter unit, while, typically, the stack is joined to the housing at such periphery by a second seal. In another aspect of this invention, the fluid inlet is positioned adjacent a first pad of the stack and the fluid outlet is adjacent a last pad of the stack, the diameter of the fibers of the last pad being smaller than the diameter of the fibers of the first pad, typically with the fiber diameter of intermediate pads generally decreasing from pad to pad in the direction of the last pad.