Elasticity, or rebound, also plays a decisive role in the quality and comfort of foam elements. It is generally expressed as a percentage. Elasticity is gauged by dropping a steel ball onto the foam and meausuring the height of its rebound. A value of 70% would mean that the steel ball has rebounded to 70% of its initial altitude. EUCAFLEX - Quality types attain on average between 40 and 50%, whereas EULASTIC HR - Quality types attain 50 to 60%.