The grey eggs are slightly denser than the purple, this allows for better support in poses similar to how a block is used. However, because of the ergonomic shape of the eggs when the hands rest in the middle and weight is tipped forward it actually decreases the angle of the wrist. This immediately releases pain from wrist conditions such as carpal tunnel syndrome while at the same time building strength through the core and back. Another great way to incorporate yoga for everybody with a small and light prop.