A cassette for supporting a film during a gaseous vapor deposition process includes a central shaft having first and second end plates. A rib on each end plate forms a spiral groove able to accept an edge of a film. Each rib has a cross sectional configuration having substantially linear major edges, a predetermined width dimension and a predetermined average thickness dimension, and a width-to-thickness aspect ratio of at least 2:1. The rib could be substantially rectangular with an optional flow spoiler at the free end or substantially wedge-shaped. The interspoke spacing between end plates is at least three hundred millimeters (300 mm) and is also greater than the width dimension of a film substrate at a gaseous deposition temperature. The width dimension of each rib is between about 0.5% to about 2.0% of the interspoke spacing.