foam grip is a soft eva foam. its squishy and doesnt hurt if it rubs against you. down side is its really sticky and its hard to move your feet around and its harder to feel the concave.
grip tape is the same stuff on a skateboard. its the perfect amount of grip. and since its not thick like foam you can feel the board and concave a lot more. downside is that you can get grip burn if you fall on the board.
no matter what grip you get, wear shoes. trust me, its better