Hybrid nanocomposite materials based on polyethylene terephthalate and inorganic flame-retardant diammonium phosphate were prepared according to the fundamental strategy of environmental crazing of polymers. Structural-mechanical modification of the initial amorphous polyethylene terephthalate and the resultant nanocomposite polyethylene terephthalate-based was carried out by rolling at room temperature. The effect of preliminary rolling on the deformation behavior of polyethylene terephthalate during subsequent stretching in air and in physically active liquid media was established.