A helmet can comprise an outer shell comprising an outer surface and an inner surface opposite the outer surface, wherein the inner surface of the outer shell comprises an integrally formed locking mechanism. The helmet can also comprise a locking liner formed of a foam material and disposed within the outer shell adjacent the inner surface of the outer shell. The locking liner can further comprise at least one side piece sized to fit between a lower edge of the outer shell and top portion of the outer shell, a top piece disposed at the top portion of the outer shell and comprising a central opening, and a rotatable foam locking piece sized to fit within the central opening and comprising a tab that is sized to mateably couple with the integrally formed locking mechanism of the outer shell to releasably couple the locking liner to the outer shell.