It's fabric-covered, square thin foam flap that is attached at the edge of the cuff. So, the back of your hand makes contact with this square pad. Your wrist and forearm are above this foam thing. Your fingers are below this foam thing.
In this picture, it is sewn to the cuff of the glove, next to the left of that flag patch. The other three sides of the square are not sewn to the glove.