as described in u s pat no 4 151 800 referring to fig2 the pbo 30 and nomex u2122 fiber 32 may be combined such that the different fibers form a gradient from nomex u2122 32 at the inner mold line face of the felt 12 to pbo 30 at the outer mold line face of the felt 12 referring to fig3 the pbo 30 and nomex u2122 fiber 32 may be combined such that the different fibers form layers with the nomex u2122 32 positioned adjacent the inner mold line surface of the felt and the pbo 30 positioned adjacent the outer mold line surface of the felt if the pbo 30 and nomex u2122 32 layers of the felt are produced separately the pbo and nomex u2122 may be combined by needling the two layers together as used herein u201c needling u201d is meant as the process of repeatedly projecting one or more barbed needles through a material such that fibers of the material or multiple materials being needled together are forced to entangle thus creating a unitary felt type body from single component materials and thus effectively stitching together multiple component materials the felt 12 is pre heat treated prior to installation upon a vehicle by first exposing the felt to incremental heat treatments which are gradually increased to about 750 u00b0 f this eliminates subsequent adverse shrinkage and allows any volatile materials to be driven off a layer 13 of coated ceramic fabric is laminated to the outer mold line surface of the felt 12 the coated fabric 13 reradiates heat away from the felt material and provides a smooth aerodynamic surface the coated fabric layer 13 is constructed of a base fabric 14 of woven ceramic.