Manufacturer page.

USG Fiberock Brand Underlayment panels and USG Fiberock® Brand Tile Backerboard panels are manufactured from an environmentally sustainable, specially engineered combination of synthetic gypsum and cellulose fibers. USG Fiberock Brand Underlayment panels have an integral water-resistant composition that offers durability, superior performance and exceptional tile bond. Both products are engineered to meet water-, mold- and indentation resistance needs under and/or behind tile, resilient flooring, carpeting, hardwood flooring and laminate flooring in new construction and/or remodeling. USG Fiberock® Brand Underlayment panels and USG Fiberock® Brand Tile Backerboard panels provide a smooth, flat surface that resists swelling and warping often seen with wood-based underlayments and tile backerboard panels, and contains none of the resins, adhesives or solvents that can stain floor covering materials. It also offers greater resistance to indentation than other underlayment and tile backerboard products and can be used in both wet and dry areas.