A blocking device for blocking a semi-finished optical element (11; 111) having a first face (14; 114) to which the blocking device (13; 113) is to be attached and having opposite to the first face (14; 114) a second face to be surfaced in a surfacing machine configured for holding the semi-finished optical element (11; 111) via the blocking device (13; 113), said blocking device (13; 113) comprising: - a mounting portion provided for mounting the blocking device (13; 113) on a corresponding mounting member of said surfacing machine; and - a blocking portion configured for blocking said semi-finished optical element (11; 111); said blocking portion comprising a support member configured for providing a rigid support to said semi-finished optical element (11; 111), said support member includes a support element (23; 123) made of a shape-memory material having a rigid state below a predetermined temperature and a plastic state above said predetermined temperature, said support element (23; 123) assuming in the absence of external forces a predetermined memory shape when heated above said predetermined temperature, said support member having a contact face (25; 125) onto which said first face (14; 114) of said semi-finished optical element (11; 111) is to be applied; characterized in that said blocking portion includes at least one of (i) a heating device configured for heating said support element above said predetermined temperature and (ii) a cooling device configured for cooling said support element below said predetermined temperature. - a mounting portion provided for mounting the blocking device (13; 113) on a corresponding mounting member of said surfacing machine; and - a blocking portion configured for blocking said semi-finished optical element (11; 111); said blocking portion comprising a support member configured for providing a rigid support to said semi-finished optical element (11; 111), said support member includes a support element (23; 123) made of a shape-memory material having a rigid state below a predetermined temperature and a plastic state above said predetermined temperature, said support element (23; 123) assuming in the absence of external forces a predetermined memory shape when heated above said predetermined temperature, said support member having a contact face (25; 125) onto which said first face (14; 114) of said semi-finished optical element (11; 111) is to be applied; characterized in that said blocking portion includes at least one of (i) a heating device configured for heating said support element above said predetermined temperature and (ii) a cooling device configured for cooling said support element below said predetermined temperature. said blocking portion comprising a support member configured for providing a rigid support to said semi-finished optical element (11; 111), said support member includes a support element (23; 123) made of a shape-memory material having a rigid state below a predetermined temperature and a plastic state above said predetermined temperature, said support element (23; 123) assuming in the absence of external forces a predetermined memory shape when heated above said predetermined temperature, said support member having a contact face (25; 125) onto which said first face (14; 114) of said semi-finished optical element (11; 111) is to be applied; characterized in that said blocking portion includes at least one of (i) a heating device configured for heating said support element above said predetermined temperature and (ii) a cooling device configured for cooling said support element below said predetermined temperature.