Abstract: Two layers of a flexible and essentially impervious material are sealed to each other at their edges and are otherwise separate from each other so as to form an interior portion. Many lengths of thread connect the layers together at numerous points throughout the interior portion. The length of the thread that is between the layers is relatively short and the thread connects the layers at a sufficient number of points to restrain the layers and hold them in a spaced relationship when the interior portion is inflated with air. Applying modest air pressure to the interior portion produces a lightweight structure of sufficient stiffness that is attached to the rear ends of truck trailers to improve airflow and reduce drag at highway speeds.