A closure for closing a bag and a die head and method for making the closure. The closure includes two closure members having support walls and mating interlocking profiles. The support walls are resilient and have self-retaining forms in vertical section including middle sections curving outwardly away from one another when mounted on a bag. Top portions of the support walls extend outwardly away from one another to form gripping panels when the closure is closed. A die head for forming a closure member includes a body that defines a slot including a support wall segment for forming the support wall of the closure member. The support wall segment includes first and second portions oriented transverse to one another and intersecting at a vertex. To form the closure member, polymer is extruded through the slot and quenched.