the kneeling garden pads are "ensolite" a closed cell foam that can be made from (at least) 3 different compositions: EPDM, Neoprene, or a combo of PVC/NBR/CR(code for vinyl, nitrile and neoprene).
Common yellow foam is PU (polyurethane) and so is the so-called "memory foam" it's just a lot denser PU with perhaps some modifiers, and it's generally OPEN cell foam.
The liquid stuff you pour into a form to make a self-skinned foam solid is also PU, AFAIK, but there may be others...