VarStiff hard/soft material via Core77:

A Spanish company called Tecnalia has developed a new type of fabric that can be made to go from soft to hard and back again. Called VarStiff, the material’s default state is soft, like regular fabric; but attaching a vacuum to an embedded valve and sucking all of the air out turns the material rigid, “[achieving] hardness equivalent to that of a conventional plastic.” To get it soft again, re-introduce air.