The present invention relates to a sealable element (1) for sealing the rim (21) of receptacles (20), the element (1) comprising at least a backing layer (2) made from a deformable material, and a sealable membrane (3) detachably connected to the backing layer (2), wherein the membrane (3) comprises an additional or integral opening means (4), wherein at least the membrane (3) has a contour with a radius varying between a lower radius value (L) and an upper radius value (U), wherein the ratio between the lower radius value (L) and the upper radius value (U) is defined by the equation 0.9≦L/u≦0.99, preferably 0.95≦L/u≦0.97. The invention further relates to a cap (10) comprising said sealable element (1) and to a receptacle (20) comprising said cap (10) being removably attached onto an opening (O).