Paper phenolic Grade XXX is a thermoset laminate constructed from a high-quality kraft paper base impregnated with phenolic resin and cured under heat and pressure into rigid phenolic sheet and rod stock. As the premium electrical grade in the paper phenolic family governed by NEMA LI-1, Grade XXX delivers the highest dielectric strength and lowest moisture absorption of any NEMA paper phenolic grade — making it the preferred choice for power distribution components, transformer spacers, industrial switchgear, and other applications where dielectric performance is critical.
Grade XXX provides 35,000 psi tensile strength, 22,000 psi flexural strength, and 13,000 psi compressive strength with a Rockwell M101 hardness. Water absorption is just 0.57% over 24 hours — significantly lower than Grade X and XX (2.00%) — which supports stable dielectric performance even in environments with variable humidity. Maximum continuous operating temperature reaches 280°F (140°C). The nema xxx designation is the recognized standard for paper phenolic in demanding electrical environments.
Standards. Grade XXX is governed by NEMA LI-1. Flammability is rated 94HB per UL 94. Test methods follow ASTM D709. The XXX designation specifically identifies the premium electrical performance tier of the NEMA paper phenolic hierarchy, distinguishing it from general-purpose Grade X and standard-grade Grade XX.
Sister grades. Step down to Grade XX — standard paper phenolic when premium dielectric performance is not required and cost efficiency is the priority. Choose Grade X — entry-level paper phenolic for light-duty general-purpose applications. When mechanical toughness in addition to electrical insulation is needed, cotton phenolic grades such as Grade CE or LE provide the appropriate combination of properties.
