Which sheet material is best for electrical insulation?

For rigid electrical insulation supplied as sheet, the main choices are phenolic paper (SRBP) for general switchgear and busbar insulation, cotton fabric laminates (SRBF) where mechanical strength is also needed, and woven glass fabric laminates (SRBGF) for the highest voltage and temperature duty. All are cut to size and machined to close tolerances. Kite Brand, the most widely used Tufnol phenolic sheet grade for general electrical insulation, is in the paper laminates (SRBP) range.