Abstract A complex relationship has been found between the combustion efficiency (χ) and its radiative component (χrad) that depends on the type of atoms and nature of chemical bonds in the fuel structure. For the halogenated fuels and polyurethane foams, respectively, the χ values increase from about 0.23 to 0.53 and from about 0.60 to 0.70; and the χrad values increase from about 0.02 to 0.30, and from about 0.30 to 0.40. For aromatic and highly unsaturated-aliphatic fuels, the χrad values are at their maximum between about 0.40 and 0.45 for the χ values between about 0.65 and 0.75. For the saturated- and moderately unsaturated-aliphatic fuels, the χ values are greater than 0.75 and the χrad values decrease with increase in the χ values. For halogenated fuels, χ and χrad values increase due to increase in the number of hydrogen atoms and decrease in the number of halogen atoms. The values increase as the nature of polyurethane foams changes from rigid to flexible. For saturated- and moderately unsaturated-aliphatic fuels, the decrease in the χrad values with increase in the χ values appears to be due to decrease in the number of hydrogen atoms and increase in the number of oxygen, nitrogen, and sulfur atoms. The profiles for smoke yield versus χ values are similar to those for the χrad values for all the fuels as expected from the soot formation–radiative emission mechanism in the flame. The following third-order polynomial regression analysis is the best fit for the data used in the study: χ rad =−2.88χ 3 +3.56χ 2 −0.510χ−0.002.