New polyurethane materials modified with rapeseed cake, a by-product of oil industry, were prepared. By using 5—25 wt. % grounded cake as additive, rigid polyurethane-polyisocyanurate (PUR-PIR) foams were produced. The mechanical, thermal and flammable properties of the foams were investigated. The obtained foams were characterized by a lower brittleness, flammability and heat conductivity coefficient than the reference foam produced using the same procedure but without addition of the biofiller.