The triangle is one of the most stable shapes in nature. A geodesic dome is formed entirely of triangles, making it a very stable structure even when it is constructed of lightweight materials such as drinking straws. Make a dome of drinking straws and see how much weight it will support. Compare it to a drinking-straw cube the same size.
Cut 35 blue straws 12cm long. Cut 30 red straws 11cm long. Tape 10 blue straws together end-to-end to from a ring. This is the base of the dome.
Tape one end of a blue straw to each end of one of the straws in the base ring. Bring the other ends of these straws together above the base straw. Tape these ends together to form a triangle. Tape one end of a red straw to each end of the next straw in the base ring. Tape the ends of these straws together to make another triangle. Use blue straws to make a triangle over the next base straw. Alternate red- and blue-straw triangles all the way around the ring. This will form ten triangles.
Tape a red straw between the top of two adjacent triangles, by taping one end to the point of one triangle and the other end to the point of the next triangle. Connect the top points of all the triangles this way, forming another ring of ten red straws. This will bring the triangles toward the centre of the dome and begin to form the dome shape.
Tape the ends of two blue straws to the right end of a red straw in the top ring. Tape the end of a red straw to the left end of the same red straw in the ring. Move around the ring alternately taping on two blue straws or one red straw at each junction of the ring. You will have five red straws and ten blue straws pointing into the centre of the ring. The blue straws will be in pairs.
Grasp the loose end of one of the red straws you just added. Move along the ring to one of the two blue straws you just added. Tape together the loose ends of these straws. Go around the ring in the other direction and tape the loose end of one of the two blue straws to the ends of the two straws you just taped together. This will form a new triangle on each side of the red straw. Continue doing this around the ring forming ten new triangles.
Tape one end of five blue straws together to form a star shape. Tape a blue straw between the ends of each of the points of the star, making a pentagon with a star in the centre. This is the top of the geodesic dome. Tape it on top of the dome, by attaching the corners to the junctions of the red and blue straws on the top row of triangles.