Material

We used heavy posterboard, and although it was tricky to cut, the results are great. You can use any type of material as long as it is rigid enough. Thin plywood or plastic would also work great. Light metals such as aluminum or thin-gauge steel would also work but keep in mind that they will not move as much as lighter mobiles.

Size

The mobile can be any size although you should make sure that it doesn't hang so low that it bumps into people's heads as they pass by. Very large or heavy mobiles will not move as much as those located in still rooms. If you plan to display the mobile in a room with a heavy breeze, then heavier pieces will be desirable since a light mobile will move around erratically.

Shape

We used a simple curved shape reminiscent of the great mobile designer Alexander Calder. You can choose any shape but if you want to achieve the cantilevered effect of this mobile, then one end of each piece must be much heavier than the other.