Pressboard and presspaper for electrical purposes. Specifications for individual materials. Requirements for pressboard, types B.0.1, B.0.3, B.2.1, B.2.3, B.3.1, B.3.3, B.4.1, B.4.3, B.5.1, B.5.3 and B.6.1|Ash (wood), Thickness, Oils, Tensile strength, Cohesion, Moisture, Shrinkage, Board (paper), Pressboard, Solid electrical insulating materials, Electrical conductivity, Density, Bulk modulus, Elongation, pH, Moulding (process), Flexibility, Grades (quality), Electrical insulating materials, Dielectric strength, Dimensional tolerances, Sulfates, Absorption, Cotton, Wood pulp, Paper products