Self-adhesive label valves are disclosed having release chimneys in correspondence of a plurality of intersection cuts in a membrane-island of film (tape) carrier (C) with cuts made in the overlying self-adhesive label made of polymeric film (E) with an adhesive layer. All are inscribed within (i.e. inside) the perimeter of the membrane-island, and are destined to overlie so as to occlude pre-formed release openings in the packaging film of heatable food, and ensure in an outstandingly reliable manner a gradual release of vapors while heating, without causing an undesirable collapse of the packaging film.