Roscoe Back Brace Lumbar Support Belt - Lower Back Brace - Fits Waists 28-39 (Medium) - Back Brace for Lower Back Pain - Promotes Correct Spine Alignment & Posture

Q: What are the stays made of?

I am not sure what you mean. There are four tongue depressor sized areas that I believe are made of plastic. These areas are covered with the same material as the brace.

Q: why does medium cost more than large, extra large

Great question - I have the large and it has all the features of the medium, so I would suspect it's a supply-and-demand price. The medium if it is in demand (or short supply) can command a higher price, the large size if overstocked you can reduce the price to move the inventory. As a reviewer the brace is great - the extra straps to clinch it tighter if necessary makes a big comfort difference between this brace and others.