A steam box can be made from PVC, plywood or hardwood. It just needs to be able to stand up to moisture and heat. Your steam box needs to have some kind of support for your work pieces inside the box so that they are surrounded by steam, not just heated on one or two sides.

How long does it take to steam bend wood?

Steaming takes about one hour per inch of workpiece thickness and parts must stay on the bending form for one hour, so unless you make more than one form, the steam box only has to accommodate one part at a time.

Does steam melt PVC?

PVC won’t melt at low pressure steam temperatures.