Abstract: The present invention is an insert that may be placed within a cap such as base ball cap or a golf cap to maintain the original shape of the cap. In one embodiment, the insert comprises a one piece flexible sheet having a centrally located longitudinal axis dividing the sheet into left and right halves that are mirror images of each other. The sheets has square shaped holed spaced throughout the sheet to provide increased ventilation. The sheet has a non-continuous peripheral edge having catch portions to prevent the insert from slipping during use of the cap. The sheet further comprises a lower portion having a central edge portion substantially perpendicular to the longitudinal axis. The lower portion comprises left and right edge portion inclined to the longitudinal axis. The lower portion further comprises a v-shaped cut-out extending inward from the central edge.