Perforated hardboard. DPI’s Signature S2S Green Core hardboard panels offer a solid foundation for finished products worldwide. Known for its unparalleled smooth surface, Signature S2S has become the standard in wood based substrates. Ultra smooth surface that resists buckling and warping. Green Core provides strength, no delamination or loose fiber. Environmentally responsible low VOC, no added formaldehyde product. Easy-to-cut and route, coat, or laminate. Flawless foundation for any product. 1/8 In. perforated holes are 3/16 In. in diameter and 1 In. on-center. 1/4 In. perforated holes are 9/32 In. in diameter and 1 In. on-center.