A novel process for the thermal stability and hydrophobicity enhancement of wood is proposed. The process concerns the impregnation of wood with water-soluble and water-insoluble salts. The salts are synthesized in situ in wood through aqueous solutions and supercritical carbon dioxide treatment. To protect salt-treated wood from absorbing large amounts of humidity a polymer film is formed upon the surface of wood and depending on the inherent roughness of wood, superhydrophobicity can be obtained. Characterization of the materials was performed by infrared spectroscopy, thermogravimetry, calorimetry, density, color and contact angle measurements and ignition and visual observations. The fire retardation is achieved in both glowing and smolding combustion and may be due to different mechanisms as it was concluded from the thermogravimetric analysis and ignition.