L sheet is the flat-panel form of NEMA Grade L cotton-phenolic laminate — a thermoset composite produced by laminating fine-weave cotton fabric with phenolic resin under heat and pressure into rigid, dimensionally stable flat stock. The fine cotton weave used in Grade L produces smoother machined surfaces and better electrical performance than the coarser Grade C and CE, making L sheet a balanced choice for small machined parts and light-duty electrical insulation.
L sheet delivers tensile strength of 18,000 psi, flexural strength of 20,000 psi, and compressive strength of 36,000 psi. Rockwell hardness reaches M105, shear strength is approximately 14,000 psi, and water absorption over 24 hours is approximately 2.5%. The material carries a UL 94HB flammability rating and operates continuously up to 250°F (121°C). These properties make L sheet a practical choice for small machined plates, terminal boards, pulleys, light-duty cams, and tooling fixtures where surface finish and machinability matter.
Standards & compliance. L sheet conforms to NEMA LI-1 Grade L and meets defense specification MIL-I-24768/15 (Type FBI). Test methods follow ASTM D709. Ready Plastics stocks L sheet in a range of thicknesses; custom cuts are available through our cut-to-size service.
Sister grades. For higher dielectric performance, Grade LE phenolic sheet uses an even finer linen weave. For higher impact resistance, Grade CE phenolic sheet uses a coarser cotton; for the lowest-cost cotton-phenolic, Grade C phenolic sheet is the standard choice. For higher mechanical strength and lower water absorption, see G-10 glass-epoxy sheet.
