This activity will teach children/students how to use nets to create 3D objects, in this case, a tetrahedron that will become a cool gift box for small items such as fortune cookies or jewellery!

To start, you will need to find a small note-sized envelope that is about 3½ inches wide by 6 inches tall. You can find these at your local dollar store. For a really colourful gift box, have the child choose an envelope with a fun design. Or, they can choose a plain envelope and decorate it however they please.

Lay the envelope flat on the table. Open the flap and press it so it stays in the open position. Using a ruler and a marker or pencil, mark a line from the left top corner of the envelope face, across to the bottom right corner of the envelope face. Do the same thing from the top right corner of the envelope face, across to the bottom left corner of the envelope face. This will create an “x”. Now mark a vertical line straight through the centre of the envelope, but stop marking once you get to the bottom of the envelope flap that you opened earlier. Now fold the envelope along each of these lines you created. Once you are finished, lay it back in the flat position.

Using scissors, help the child cut the top of the envelope off. To do this, cut along the top of each diagonal line, starting at the top left of the envelope face, and continuing until you reach the top right of the envelope face. This will discard the flap and the top triangle of the envelope.

Now for the tricky part. Open up the envelope by pulling from both end triangles. The bottom triangle on the envelope face with the vertical line through it, will act as the base. Flatten this gently, and you will see the envelope start to take a 3D shape. Now take the left side of the envelope, which will look like a triangle, and tuck it into the right side, which will also look like a triangle.

Keep adjusting and flattening the edges until the two triangles fit perfectly into each other, and you have created a 3D shape – a tetrahedron. Have the child decorate their tetrahedron into a gift box, or use markers to turn it into an animal like a bird or a fish!

To put a gift inside the tetrahedron, simply pull the triangles apart, and place the object inside. Be sure to have the child secure it with tape or glue so the gift doesn’t fall out.

This activity will reinforce the child’s understanding of common mathematical solids – nets are featured as tools for representing shapes in two dimensions.