This is the amount of energy that is stored by a material and causes it to "bounce back" after a weight is removed. It is also connected to how quickly the material bounces back. It is measured by dropping a ball on a material and measuring the height of the bounce as a percentage of the height from which it was dropped. Higher resilience polyfoam is often higher quality than lower resilience polyfoam and resilience is an important part of both the feel of a material and it's ability to allow freedom of movement.