A safety helmet is disclosed having a shell and a comfort liner coupled to the inner surface of the shell. The comfort liner is constrained to the front part and to the rear part of the shell, and the helmet has a webbing arranged between the shell and the comfort liner along the upper median portion of the comfort liner. The webbing has a front end constrained to the front part of the comfort liner and a rear end to move the webbing with respect to the shell and cause consequently the change of the overall dimensions of the comfort liner inside the helmet. The webbing is constrained, with respect to the shell, in an operative position corresponding to the overall dimensions of the comfort liner inside the helmet.