scrim layer 26 to the batt back side 16 in such a way that it spans the corrugations 18 the scrim 26 imparts additional stiffness and shape retention properties to the headliner 10 the scrim 26 does this by structurally reinforcing and holding the shape of each corrugation 18 against bending forces that might be applied to the headliner 10 as is best shown in fig2 the bonded scrim layer 26 34 caps off 34 each corrugation channel 20 to form an elongated trapezoidal 34 torsion box 34 structure that resists bending and twisting forces full density extruded pet 27 fills each corrugation channel 20 between the batt back side 16 and the scrim layer 26 the full density extruded pet 27 is heat bonded to the low melt fibers in the batt 12 the parallel rows of elongated full density extruded pet filler material 27 follow the general curvature of the headliner 10 and act as structural arches supporting the concave shape of the headliner 10 after installation while the first and second embodiments include corrugations 18 formed into the batt back side 16 as shown in fig3 variants of the first and second embodiment may additionally or alternatively include corrugations formed in the batt front side 14 within the scope of this invention other variants may also include in the place of corrugations 18 a plurality of closely spaced craters that define an 34 egg crate 34 type surface across the batt back side or front.