Abstract: The invention relates to an element with a determined permeability, said element comprising a first layer and a second layer welded together with interposition of a band of fibers, so as to form a plurality of adjacent welding points, which are separated the one from the other, the fibers of the band having a melting temperature at most 5° C. higher than the melting temperature of at least one of said layers, whereby at the welding points, fibers of the band are molten into the welding lines, so that between two adjacent welding lines, fibers of the band are not molten and form a channel for the exchange of gases but avoiding the passage of solid particles.