AbstractFlammability, smoke evolution, thermal, and thermomechanical properties of low‐density rigid polyurethane foams obtained from different aromatic polyols were investigated. The foams were prepared according to a standard formulation ensuring the same foam phosphorus content. Cellular polyurethanes with the best fire resistance were obtained from polyols containing disubstituted naphthalene and biphenyl rings. A linear equation was proposed to describe the influence of various structural units of the polyurethane (the content of cyclic structuresCc, nitrogen contentCN, and crosslinking equivalentMc) upon its flammability, expressed in terms of its oxygen index (OI)documentclass{article}pagestyle{empty}begin{document}$$ {rm OI} = B_0 + B_1 C_c + B_2 C_{bf N} + B_3 left( {{1 mathord{left/ {vphantom {1 {M_c }}} right. kern-nulldelimiterspace} {M_c }}} right) $$end{document}Thermal stability of crosslinked polyurethanes was not found to influence significantly their thermomechanical properties, while crosslink density and the type and quantity of cyclic structures additionally introduced did have a pronounced effect upon these propertie
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