This specification covers electrically insulating, unbleached sulfate paper and paperboard used as layer insulation in coils, transformers, and other similar apparatus. The materials may also be used as turn insulation, slot liners, wedges, phase insulation, and separator papers in stranded wire/cable constructions. This specification does not include tissue for manufacture of capacitors. Other commonly used terms for the materials include soft coil wrap, dense coil wrap, kraft coil insulation, dry-finished kraft, and water-finished kraft. The materials covered in this specification are classified into four types according to density range and nominal thickness and should conform to the required values of ash content, alcohol-soluble material content, aqueous extract conductivity, water-soluble chloride content, fiber composition, moisture content, hydrogen ion concentration, pH, tensile strength, dielectric breakdown voltage, and conducting paths.