Abstract: A neutron protection thermal insulating material is obtained by adding a boron compound and, if necessary, a hydrous compound, to chrysotile asbestos fibers. To form the material, the asbestos is opened with the use of a surface active agent in the presence of water. The boron compound is added and air bubbles are incorporated into the mixture which is then dried, molded and compressed. The resulting product is characterized by a construction wherein the opened asbestos fibers are oriented in substantially parallel relation to each other and in the direction perpendicular to the compression direction and air pockets are flatly arranged between the fibers and substantially parallel thereto to reduce thermal conduction through the material in the direction parallel to the direction of compression.