I have enough cloth left over to make another set so I am going to do an experiment.
In this first set of bellows the inner and outer cloths are only stuck together by the adhesive on the stiffeners. they are free to move away from each other in the surrounding areas although the folds will most likely keep them together.
I want to make another set with the outer cloth laminated in the same way but with a piece of adhesive over the whole of the inner cloth so the two are also joined together in the areas around the stiffeners.
I don't know if it will make any difference but I will find out soon!