What os the purpose of a free body diagram

To show all the forces acting in a body due to contact with other objects, and/or due to body forces acting on the body (such as gravity).

I think the correct answer would be that synthetic polymers are lightweight. One benefit of using man-made polymers would be that they are lightweight as compared to natural polymers. Another benefit, would be that properties of these polymers can be easily manipulated since they are made by human.