Two methods of temperature field reconstruction starting from refractive index map obtained with Moire deflectometry in downward flame spread along cylindrical PMMA samples have been compared, in order to determine their suitability in this kind of combustion problems, i.e., diffusive flames on solids. This article shows the applicability of the method based on the hypothesis of the same functional behaviour (SFB) of all the variables representing the flow, which provides a good picture of the temperature field. However, the method based on numerical solutions of the Navier-Stokes equations with simple chemical kinetics, suitable for other purposes, does not provide reliable quantitative results when it is used for the computation of the spatial variation of the Gladstone-Dale (G-D) constant and the gas constant, and for the later evaluation of the temperature from the refractive index map.