How do you stiffen fabric?

It was recommended on WebMD to place a piece of plywood between the boxspring and mattress. However, you can also try rotating and flipping the mattress. If it is more than ten years old, you will do best to replace it. Box springs do not need to be replaced if you are purchasing a same size mattress.

Never use plywood to stiffen a mattress. If it is too soft, the it is worn out. Replacing it is the only solution.