[MetalMan]

Is this for your Rustler? If you are doing only a lower chassis plate with no upper deck (besides the one at the front), then 9mm or 10mm might work (anything less will flex too much). If you are doing a full upper chassis plate, then you could use 6mm (1/4") on the top and bottom.

The chassis I'm doing for my Rustler is 1/4", and will have vertical pieces that go on the outer edges of the chassis (surrounding the battery) to make the chassis stiffer. The idea is that the chassis will be very stiff, but since it's polycarbonate it should still give a little in the event of a crash.