Abstract
This article presents an innovative approach to the flame retardancy of rigid polyurethane foams using natural waste in the form of buckwheat hulls in combination with an inorganic additive-perlite. A series of tests were presented in which various contents of flame-retardant additives were used. Based on the test results, it was found that the addition of the buckwheat hull/perlite system affected the physical and mechanical properties of the obtained foams, i.e., apparent density, impact strength, and compressive and flexural strength. The structure of the system had also changed, directly affecting the hydrophobic properties of the foams. In addition, it was observed that the addition of buckwheat hull/perlite modifiers improved the burning behavior of composite foams.