Q: How much can we bend 3/8-inch plywood forms?

A.: Probably to a circle with a 3-foot radius if you bend across the grain, or a circle with an 8-foot radius if you bend parallel to the grain. Even shorter radii can be used if the panels have no knots and have a short grain, or if they are wetted or steamed. Some panels might undergo a localized failure at excessively short radii, however. The American Plywood Association gives the following minimum bending radii:

¡ Bending Radii
Plywood thickness 1/4″ 5/16″ 3/8″ 1/2″ 5/8″ 3/4″
Across grain 2′ 2′ 3′ 6′ 8′ 12′
Parallel to grain 5′ 6′ 8′ 12′ 16′ 20′