range from about 0 5 to about 30 microns for this shape and size of filler the particularly preferred materials are glass silica carbon and graphite another shape of particle useful as a filler in the present invention is fibrous particles having a diameter of from about 0 5 to about 10 microns and a length of from about 10 to about 20 times their diameter materials preferred for this size and shape are glass carbon graphite and aluminum silicate another shape of filler preferred for use in the present invention is the flake shaped particle having a maximum thickness of from about 0 25 to about 5 microns and a maximum surface dimension of from about 4 to about 20 times the maximum thickness of the flake shaped particles materials preferred for flake shaped particles include glass mica carbon and graphite by describing the barrier coating as 34 porous 34 it is meant that the barrier coating used in the present invention should have a controlled porosity such that there is produced an interconnecting membrane structure through which the materials entrapped within the coating can permeate so as to prevent delamination blistering rupture or other types of failure but yet so low that the utility of the barrier is not significantly affected i e so that.