A protective seal cap assembly for enclosing an end portion of a fastener extending through a structure, which includes a cap member. The cap member includes a sidewall which defines an opening and defines an interior space within the sidewall and aligned with the opening, wherein the sidewall defines a central axis. The cap member further includes at least one rib which extends away from an interior surface of the sidewall within the interior space and extends in a direction along the central axis of the cap member.