This paper describes the results of quantifying gaseous chemical compounds in smoke, which were obtained from thermal degradation analyses of rigid polyurethane (PU) and rigid polyisocyanurate (PIR) foam. The analytical method used was evolved gas analysis, which consisted of a combination of two different analytical methods: thermogravimetric/differential thermal analysis-Fourier-transform infrared spectroscopy (TG/DTA-FTIR) and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS). A lack of specific internal standards for measuring the released gases in thermal degradation analyses was solved by introducing a mathematical formula to indirectly determine the absolute mass values for the chemical compounds of interest. The combined method allowed for the quantification of absolute masses of the released gaseous chemical compounds in the smoke without the use of internal standards. This method has the potential to be used in quantifying gaseous chemical compounds in other foam materials as well.