Residual softwood was thermomechanically pretreated and used to produce composites with no synthetic binders. The lignocellulosic material was steam exploded with a thermomechanical aqueous vapor process in a continuous tubular reactor. The study attempts to use the intrinsic bonding capacity of the steamed fiber, which is due to the plastification of the lignin. Chemical and structural changes in the pretreated substrate were evaluated by analytical characterization and scanning electron micrographs (SEM). The effect of the pressing conditions was evaluated in accordance with the physicomechanical responses of the composites. The physical and mechanical properties of the panels obtained were tested using UNE EN Spanish standard-European standards. In order to get more information about the degree of adhesion between the lignin and the fibers, SEM micrographs were taken of the broken surfaces of the material tested by the internal bond method. The results show that the thermomechanical pretreatment, pressing temperature, and time have a great effect on the mechanical and physical properties of binderless composites. The steam explosion aqueous vapor pretreatment is a good way for conditioning softwood sawdust for production of composites.