Backrest for armchairs

Improved backrest for seats, of the type formed by an assembly (1) comprising a correspondingly coupled front soft body (1.1) and a rear shell (1.2), with a headrest (3) in the upper part comprising a respective front soft element (3.1) and a respective rear shell (3.2), characterized in that the front soft body (1.1) of the backrest assembly (1) defines a notch or recess (11) in the upper part, where the front soft element (3.1) of the headrest (3) is fitted, establishing the subjection of said front soft element (3.1) of the headrest (3), with respect to the corresponding rear casing (3.2), by means of retention hooks in the upper part and a lower screwed tie that is established through the rear shell (1.2) of the backrest assembly (1).