According to requirements of aviation norms depending on functional purpose of material, samples at carrying out tests for combustibility are exhibited at vertical orientation by burner flame within 12 or 60 seconds. Often there is need of performance of qualification tests at both modes of exposure. For the purpose of reduction of volume of tests foreign researchers have makes the decision that 60-second tests are more rigid and compliance to this requirement automatically means also implementation of the requirement for 12-second dough. Researches on influence of duration of exposure by flame was conducted at testing samples of polymeric materials and core panels on flammability characteristics (burn-out length, duration of residual independent burning) and the obtained data are analyzed. It is shown that at 60-second exposure test burn-out length always more than at 12-second. For thick materials (thickness more than 3 mm), as a rule, duration of residual independent burning at 60-second exposure are more than at 12-second. However, for thin materials (up to 1 mm thick) duration of residual independent burning at 12-second exposure are more than at the 60-second. Thus, materials corresponding to requirements of tests for panels of walls of passenger cabin may not satisfy to norms of fire safety for materials of auxiliary rooms and cabin of pilots. Therefore, for thin materials application of rule about absorption of results 12-second tests by 60-second is inadmissible.