These boards were tested by dropping steel balls of increasing weights on standard breaking boards. The weight required to break a board of the same width varied widely from board to board. An average was taken and the boards were developed to break at that point.
And they do, at the first break and the one thousandth, these boards take the same force to break.
All the boards are stackable for multiple-board breaks. The boards have padding on the back, so that if someone is holiding the board for the break it is more comfortable for them.