Our pull out tray System B is made out of a very rigid aluminum frame as well as a very high grade aluminum laminate panel for the bottom. Assembly is required. System B is intended for sizes where System A is not available for, cages that will not have a pull out floor, cages with more weight than System A, and cages that will be outdoors. If you need help deciding, please call and a customer service representative will help you decide which system is for you.