This paper concerns the problems of designing the light, fireproof, temperature stable and manufacturable neutron-absorbing materials and also shows the way for solving these problems. In the case of using the Astralenes it is possible to increase the irradiation stability of polymer components of the composite neutron-absorbing materials. In that way it is possible to bring its mobility to the level of self-packed material (R9) with a minimal amount of carboxyl plasticizer (0,16% wt). There is an opportunity to create the new composite having no equal analogs for the combination of properties, including the amount of hydrogen (0,05-0,06 g/cm3) in the wide range of the temperature. It is found that using the modified polymer components in the composite neutron-absorbing material in quantity not exceeding 12% wt does not exclude these compounds from the class of noncombustible materials. For the first time the method of increasing the mobility of working mixture is tested on magnesium matrix with using modified carboxylate hyper plasticizer, that allowed to get a qualification of neutron-absorbing material R9 with amount of modified plasticizer less than 0,16% wt. Neutron-absorbing material, created on the basis of the research, exceeds known analogs in combination of specific weight, manufacturability, fire hazard class and specific content of hydrogen at elevated temperatures.