Abstract: A closure mechanism for use with bag- or sachet-like packaging which is substantially formed by opposing sheets of polymeric material; wherein said closure mechanism includes first and second sets of opposing substantially parallel ridges, said ridges defining complementary grooves therebetween that are adapted to receive said opposing ridges in a form-locking engagement; wherein the surface of said ridges and grooves feature a plurality of ribs extending traverse and from said surfaces such that, when said first form-locking engagement is made, the ribs extending from said ridges tend to interfere with the ribs extending from said grooves thereby to impede unintentional opening of said closure.