Hey Jim, Renshape is a lightweight composite/wood material that is as lightweight as balsa wood but much more durable and easy to work with in regards to shaping parts for model use or casting. The one downside is that it is not the cheapest material out there.
Try www.freemansupply.com they have a starter/sampler kit that only retails for about $25, and it includes multiple pieces of different grades of Renshape
Thanks so much Wayne !!!