Polyurethane-Phase Change Materials (PU-PCM) composites are used for thermal regulation aiming to conserve and efficiently manage thermal energy. These materials combine the properties of PU, such as low thermal conductivity, low density and excellent mechanical properties as a thermal insulator, with the benefits of PCM allowing thermal energy storage, which greatly reduce energy consumption in heating and cooling. Adding a flame retardant to the PU-PCM composition improves fire resistance. The objective of this study is the preparation and characterization of a composite material based on PU rigid foam containing 30% by mass of commercial paraffin waxes as PCM, together with magnesium hydroxide as flame retardant. A series of samples were prepared by incorporating different percentages of Mg(OH)2, ranging from 1 % to 5 %, with and without the PCM. Various thermal and chemical characterization tests were carried out. The results indicate that the structure of the PU cells is not affected by the increase of the Mg(OH)2 incorporation rate. In terms of thermal properties, the addition of 1% flame retardant increases the latent heat from 25.9 J/g to 39.68 J/g. As the amount of Mg(OH)2 incorporated increases, the flame retardancy increases.