A closure system can include a body member, cap member, and flexible hinge member joining the body and cap members. The hinge member includes a pair of hinge portions with an opening between them. The hinge portions can include substantially planar segments of uniform thickness, providing hinge portions with uniform thickness along their lengths when the closure system is in open and closed configurations. When the closure system is fully opened, the hinge portions can extend axially between the body and cap members when viewed from above, the substantially planar segments can include end segments that are substantially coplanar to each other and a central segment that occupies another plane parallel to that occupied by the end portions, giving the central portion of the hinge portion an elevated orientation relative to its end portions, or the appearance of a hump when viewed from the side.