Six types of heat resistant synthetic electrical insulating papers (A-insulating papers), which belong to thermal H-class, named A-Board, GA-Paper, A-Tissue, A-Mica Paper and A-Mica, were developed to meet various requirements. They were made of pulp like materials such as fibrids and fibres made from aromatic polyamide, fribrids and glass fiberes or mica platelets.These A-insulating papers have following characteristics and end-use areas.1) A-Board, designed for the electrical insulating board of special A-class rolling stock transformer for the electric trains of the Nationwide New Line of Japanese National Railway, has high physical and electrical properties, excellent moldability and uniformity in density and thickness. It is also suitable for the insulating board of dry type transformers.2) GA-Board, composed of fibrids and super fine glass fibres, is characterized by its easy varnish and oil impregnability, punching quality and high dimensional stability. It is used as the insulation board for dry type transformers.3) GA-Paper, composed of fibrids and super fine glass fibres, is characterized by its good varnish impregnability and holdability and high dimensional stability. It is suitable for a substitute for electrical insulating asbesto sheet and the good layer insulation sheet for rotating machines.4) A-Tissue, thin leaf insulating paper made of only aromatic polyamide fibrids, is characterized by its very high dielectric strength and high flexibility. It is suitable for the wrapping tape for a wire insulation.5) A-Mica Paper, flexible mica sheet combined mica platelets with a few wt.% of fibrids, has good handling quality, because fibrids grasp and hold firmly mica platelets. So it is used as very good basic material of mica paper tapes as insulation for high voltage rotating machines.6) A-Mica, laminate paper thermally bonded without any adhesives A-Mica Paper and aromatic polyamide paper (backing) into a single sheet by hot calender, has excellent electrical properties and corona resistance due to high mica content and uniformity. It is adopted as the good insulating sheet for high voltage rotating machines.