If you use our design tool and/or download our templates, you’ll see that the parts are divided into two or three kinds: (1) Gears, (2) Case, and (3) Linkages. We suggest using different types of paper for each.
First, if you choose to build your model with mechanisms including gears with teeth (e.g., rack and pinion gears, spur gears, or planetary gears), we suggest to use a rigid type of material such as (A) illustration board or mat board. Compared to (B) cardboards or (C) foam boards, the higher density and rigidity of (A) make the gear stronger. Also, in order to make sure that gears interlock, we suggest attaching at least two layers to make the gear thicker. If you choose to include mechanisms that have gears without teeth (e.g., cam, crank, or Jansen mechanisms), you can use the same material as the case.
Second, for the case parts and gears without teeth, we suggest using cardboard. You can also use foam board instead but foam board is more expensive than cardboard, which you can often find for free. Depending on the type of cardboard, however, the thickness can vary from 2mm to 5mm. So you may need to adjust the assembly instructions such as the number of layers to attach for interlocking gears.
Third, if you choose to build movements such as open-close, flapping, or walking, your file may include folding nets to build linkages. We suggest using any type of thicker paper that your printer can handle. It’s okay to use normal office paper, but the linkages will bend because they aren’t not strong enough to push up the upper part. You can find thicker paper for your printer at any office supply store.