Abstract: A shutter system for a portal opening such as a window or door including a flexible barrier made of a plurality of interlocking flexible barrier slats having stop elements attached to barrier slat ends, a mounting assembly having guide tracks disposed on each side of the portal opening and a retention assembly having retention surfaces fixedly attached to the mounting assembly facing away from each end of the barrier at an acute angle for engaging the stop elements such that when displacement forces cause the flexible barrier to flex, the stop elements are displaced to engage the retention surfaces at an initial angle to anchor the ends of the flexible barrier within the guide tracks such that the engagement angle decreases as the flexible barrier flexes further until the stop elements flushly engage the retention surface.