An inflatable curtain airbag is secured along an upper edge to a body structure of the motor vehicle and deploys downwardly when inflated. Prior to deployment, the lower edge of the curtain is not tethered to the vehicle body. When nearly or fully deployed, the lower edge of the curtain engages an adjacent part of the motor vehicle so as to form a virtual tether therebetween resisting relative movement between the curtain and the adjacent part.