Thermal degradation of rigid polyurethane foams chemically, modified by polyhedral silsesquioxanes was analyzed using hyphenated techniques - thermogravimetry (TG) coupled with FTIR spectroscopy and quadrupole mass chromatography (QMS). Two functionalized POSS were used - PHI-POSS as pendant group to the main PU chain and OCTA-POSS which acts as a chemical crosslinking agent due to the presence of eight OH-terminated side chains. Based on thermogravimetric data, thermal stabilization effect of POSS particles on PU foamed matrix was found and it was evidenced by shift of the initial decomposition temperature. The TG/FTIR/QMS studies showed that the thermal decomposition of polyurethane foams reinforced with POSS starts from about 150 degrees C via urethane linkages scission. In lower temperature region the materials decompose to some low molecular weight compounds and intermediates with ether/ester and alcohol groups. At the temperature above 350 degrees C evolution of hydrocarbons, aldehydes, alcohols, ethers, glycols, amines, cyclic species and low molecular weight compounds-carbon monoxide, carbon dioxide, water and ammonia was recorded. The evolution profiles,of degradation,products proved that POSS influences the mechanism of PU decomposition. (C) 2016 Elsevier B.V. All rights reserved.