Simple curves in formwork sheathing can be made with dry plywood down to a radius as small as 24 inches. Tighter curves can be formed by selecting panels with clear knot-free straight grain, and by wetting or steaming before bending. In bending or other form building work, it is important to remember that plywood strength depends on the direction in which it is placed on its supports. When the grain of the plywood face runs at a right angle to the supporting joists or studs, it is said to be used the strong way. For best results in bending, provide smoothly curved supporting members such as 2x stock cut to the proper radius less thickness of the plywood panel.
Thick plywood, like solid timber, may also be bent by sawing slits or notches--referred to as kerfing--in the panel on the inside of the curve.