Embodiments are disclosed for headwear including a crown and an elasticizing kit, the elasticizing kit including a double-sided sew flange, the double-sided sew flange having a first terminating end opposite a second terminating end, each of the first and second terminating ends including a respective slot for inserting material, a size-adjusting mechanism including at least one strap and adapted to selectively adjust a size of the headwear, the size-adjusting mechanism being coupled to the double-sided sew flange, and an elastomeric strap coupled to the size-adjusting mechanism, the elastomeric strap being attached directly to the slot of the first terminating end of the double-sided sew flange or the slot of the second terminating end of the double-sided sew flange.