The authors investigate the fire-protective efficiency of a basalt roll material, which is used for light steel thin-walled structures. The values of fire-protective efficiency for the steel C-shaped profiles without fire protection made of basalt wool material MBOR-F were obtained in the experimental and numerical studies. This article presents the estimated dependence of the thickness of the fire-protective material MBOR F on the resistance to fire with regard to light steel thin-walled structures. The approximating functions are formed on the basis of the experimental data and presented as nomograms for heating of the steel structure. There was an absence of the samples’ deformation and destruction of the fire-protective material during the fire tests. This allows us to conclude that the fire-protective efficiency of the light steel thin-walled structures increases by 2–4 times. Implementation of the study results will expand the scope of fire-protective materials for the light steel thin-walled structures, improve the quality of fire protection projects for buildings and constructions, and help ensure the fire safety of structural elements.