In this thesis we have dealt with issues of thermic resistance of retardantly modified wood material specifically of spruce wood and pine plywood exposed to radiant heat. Theoretical part of the thesis is composed of file about findings of hardwood as well as about materials on the basis of wood,its features, (including fire-technical) and ways of their evaluation from the fire-technical point of view, as well as about improving of these features through protective retardant substances. Practical part contains experimental evaluation of unprotected and retardantly modified (by substance Bochemit Antiflash) samples of spruce wood and pine plywood under a load of radiant source of heat. The essence of evaluation was to find out influence of effectiveness of protective substance from the point of view of used concentration and amount of coating of this substance. Evaluation of results shows that used concentration and changing ways of coating has a significant impact on evaluated fire-technical features. More specifically, application of 50% dilution on the samples of spruce wood is difference between unprotected samples and retardantly modified 3-layer coating almost 19%. When using 100% concentration, the difference is almost 65%. On the samples of pine plywood with application of 50% dilution, the difference between unprotected and retardantly modified samples with 3-layer coating is 26%. When using 100% concentration, the difference is roughly 19%.