At one time or another you may have folded a flat piece of cardboard into a gift box, or maybe a box for mailing a package. The flattened box may have had creases to show you where to fold in order to create the sides of the box. In this way, you had taken a two-dimensional flat object and changed it into a three-dimensional object. But the amount of cardboard did not change! So, to find the amount of cardboard the box is made of, you could simply find the area of the unfolded box.
In the activity, Surface Area of Triangular and Rectangular Prisms, students find the surface area of triangular and rectangular prisms by adding the areas of the faces of the prisms. They use flattened out prisms called nets to help them figure this out. The dynamic nature of this activity allows students to fold and unfold prisms to help them see the two-dimensional net of the prism as well as the three-dimensional solid.