Abstract This work aims to develop a new composite material to improve the thermophysical properties and the lightness of gypsum plaster made with date palm fibers for the purpose of reducing the building energy consumption. This composite material is intended to be used in walls or false ceilings. Date palm fibers- gypsum boards could be used instead of plaster boards as thermal insulators in buildings. By varying the mass fraction of date palm fibers (from 0 to 20%), an experimental investigation of the thermo physical proprieties of gypsum reinforced with date palm fibers was mainly performed using the periodical and flash methods which were coupled to an inverse technique. The experimental results of thermal conductivity showed a good agreement with the theoretical model developed by Woodside and Mesmer for the determination of equivalent thermal conductivity.