20" x 4.5" Big Blue Whole House Sediment Filter is made of fine melted polypropylene, which is blown and spun in a cylinder-like form. The primary function of a sediment filter is to remove large and fine particles from drinking water, such as sand, dirt, silt, and rust particles. These filters have graded density layers, meaning the outer layers are more porous, catching larger particles, while the inner layers are finer microns catching smaller particles.