As mentioned above by Vitas and Ayrtek, Poron XRD is a Urethane open cell foam, it's been around since the 60's at least and has often been used for the absorption/deceleration of force.
For human use (its hugely used in telephone keypads, laptops etc..) in sport the ideal situation is slowing down and reducing the risk of injury to a smaller object hitting a larger object. If you google Poron XRD it's widely accepted as a leader for such products as kneepads, protective bike pads, equestrian vests, insoles for comfort but not sport as the return is non existant (as it is designed to absorb).
So it means, if you fall on your knees on a larger mass (eg earth) then you will be protected. But if a smaller item hits you (eg ball) the ball will be protected. It's something to be very careful with as although anything will help to a degree, (fag packets in the pocket or an old beer mat for a thigh pad for example !) one has to understand the principle function of a component thus its ideal use. You ideally want to reflect the energy away from the body and not absorb it towards the body.
PS this is just a general thought and not in any way a dig at products.
Cheers !