A retractable barrier includes a rollup or otherwise retractable panel that can extend between two spaced apart support members. When not in use, the panel can retract onto one of the support members to permit passage. The barrier provides substantial impact resistance by having the reactive force of the impact transfer directly between the barrier's retractable panel and its support members without having to rely on the strength of the panel's take-up roller or the strength of the roller's anti-rotation mechanism. This can be accomplished by having a slot-engaging stop member mounted directly to the panel itself. The stop member is preferably a pipe, rod, bar or some other vertically elongate member that can broadly distribute an impact reactive force over the height of the panel. In some embodiments, the barrier can be set for various doorway widths by simply repositioning the stop member's location on the retractable panel.