This paper addresses the problem of multi-robots object transportation by using the concept of object closure. In contrast to form or force closure which is used in the research of grasping, object closure is a condition under which the object is trapped so that there is no feasible path for the object from the given position to any position that is beyond a specified threshold distance. Once object closure is achieved, the robots can cooperatively drag or flow the trapped object to the desired goal. In this paper, we address the concept CC-closure object, which is used for efficient testing of object closure. Testing algorithms using these properties is described. Also object closure margin is defined and the scaling and control problem of the caging formation is addressed. Finally, an example of object closure constructed from both bodies and hands of mobile-manipulators, which have different shape and size, is discussed and experiments are presented for illustrating the proposed concept.