The shrivel flap is a Velcro backed closing flap. It is named for a feature that allows it to "shrivel" or peel from the opposite end in the event that it is subjected to shear forces on deployment. The advantage to this is that Velcro requires up to 40 times less force to peel than to shear. It so happens that a head down deployment will subject the Velcro flap to shear forces. A shrivel flap is a necessity on a Velcro closed rig.
In 1998, Consolidated Rigging was the first to introduce the "tuck-shrivel-flap" on the Perigee II. This unique design combines the safety of a classic shrivel flap with the added security of a tuck-flap. This protects the top edges of the flap from unintentional snags and/or high speed airflow. Both of which can lead to a premature deployment.