Abstract: A process for thermoforming a plate-like element (10) of composite polymer material, in which a central region (11) and a peripheral region (12) are defined, comprising:—providing a mould (1) including a male member (3) and a female member (4) which may be displaced between an operating position in which they are pressed against one another, and a non-operating position in which they are spaced from one another,—disposing said plate-like element(10) on said mould such that its central region (11) is interposed between said male member and said female member and holding it at its peripheral region (12) while said male member (3) and said female member (4) are displaced towards the operating position in order to abut against and deform the plate-like element,—completing the displacement of the male member and the female member into the operating position and maintaining them in that position for a predetermined period of time,—displacing the male member and the female member into the non-operating position in o