<p>A valve comprising a grommet (3) and a stem (4), the grommet comprising a tubular member (6) having an outwardly extending radial skirt (7) at one end, said grommet being manufactured in a single material, characterized in that said material has a hardness ranging between 80 Shore A - 90 Shore A and in that the valve has a gas loss of less than 5 grams per year.</p>
