A thermally and hygroscopically stable subsurface layer for supporting an outer (typically visible) surface of an acoustical panel. The subsurface layer comprises a thermally and hygroscopically stable composite, specifically a non-woven or woven fabric impregnated with binder and filler materials. The fabric provides exceptional resistance to thermal expansion and contraction, while the binder and filler materials are naturally very resistant to moisture changes. The result resists warping, cupping, or bowing in response to changes in ambient moisture or temperature, especially in situations in which the laminated surface and subsurface layers are perforated to allow sound to enter the interior or the panel and be absorbed by suitable materials within the panel.