Hard to say not knowing what kind of design you are developing. I have some friends who worked for Dansk and they would often use poplar and balsa woods to work through designs. You could also use one of the lighter density reshape urethane boards. For quicker studies, you might try strucs foam (structural foam) or balsa foam. I have a friend that did some utensils for Alessi and he did them in clay at 200% scale initially.