The invention relates to a packaging, preferably for foodstuffs, said packag ing comprising a container and a lid, both of which is made of a material which is suitable for injection moulding, said lid being sealable relative to the container; and wherein the lid comprises an elevated portion for abutment on the internal, upper edge of the container, wherein at least a portion of the lid (2) is made with a sealing zone (7, 8) for joining with the container (1 ), said sealing zone (7, 8) being added with an active material which, by influence during joining, changes the material in the sealing zone (7, 8) to the effect that the sealing becomes weaker than the surrounding material, whereby the sealing is, upon opening, broken in the joint and not in the surrounding material. The invention also relates to a method of sealing the above packaging, wherein a material is added which, during the sealing procedure, changes the material in the joint to the effect that the seal becomes weaker than the surrounding material, whereby, when opened, the seal is broken in the joint and not in the surrounding material.