The invention relates to the manufacturing of solid wood doors and consists in increasing the insulating value of a door by inserting an insulating material between the internal and external panels and in the center of the structural parts of the door. In this way, a door with a minimum of non-insulated surfaces is achieved. By using this system, the insulating value of the assembled door is significantly increased and reach the requirements of high energy efficiency programs such as ENERGY STAR™. In addition to this, the rigidity and the durability of the solid wood door are not significantly compromised. A door with a traditional style and high thermal resistance levels is achieved.