XXX sheet is the flat-panel form of NEMA Grade XXX paper-phenolic laminate — a thermoset composite produced by laminating high-grade paper with a specially formulated phenolic resin under heat and pressure into rigid, lightweight flat stock. Grade XXX is engineered for improved dielectric performance under humid conditions compared to standard XX, making XXX sheet a smart choice for terminal boards, radio-frequency insulators, and switchgear panels in environments where moisture exposure is part of normal service.
XXX sheet delivers tensile strength of 14,000 psi, flexural strength of 16,000 psi, and compressive strength of 26,000 psi. Rockwell hardness reaches M105, shear strength is approximately 11,000 psi, and water absorption over 24 hours is approximately 1.8% — roughly half that of Grade XX. Dielectric strength is approximately 650 V/mil short-time at 1/16″ thickness, with markedly better insulation resistance after humid conditioning than XX. The material carries a UL 94HB flammability rating and operates continuously up to 250°F (121°C). These properties make XXX sheet a strong choice for terminal boards, switchgear panels, RF insulators, and electrical equipment where humidity tolerance matters.
Standards & compliance. XXX sheet conforms to NEMA LI-1 Grade XXX and meets defense specification MIL-I-24768/13 (Type PBG). Test methods follow ASTM D709. Ready Plastics stocks XXX sheet in a range of thicknesses; custom cuts are available through our cut-to-size service.
Sister grades. For lower-cost paper-phenolic in dry environments, Grade XX paper-phenolic sheet is the standard choice. For higher mechanical and impact strength, Grade C cotton-phenolic sheet or Grade CE cotton-phenolic sheet are preferred. When higher mechanical strength, lower water absorption, and significantly better dielectric performance are required, step up to G-10 glass-epoxy sheet or, for flame retardance, FR-4 glass-epoxy sheet.
