Processes like thermal expansion produce very slight expansion/contraction. I am looking for a material/process that expands significantly, say 10% to 20%, in the room temperature range while maintaining its' shape. I know some materials expand significantly when wet, but don't know any numbers or where to locate such data. It would be bonus if the material could be put in a mold. I am doing an art project and would like to scale up some of the elements I am using.