This is a type of knot is known as “tritangentless” because there are no planes which are simultaneously tangent to three distinct points on the curve. Being tritangentless means that the curve can never have more than two points touching the flat surface at any given time. This is what makes models of tritangentless knots roll.
The knot can come in different shapes and proportions, but this model minimizes the vertical variation of this center of mass making it the best proportion for rolling.
The model is provided in a “textured” and “plain” version. In the “textured” version there is a small point of contact where the knot crosses, making it strong enough for your kids or cat to play with.