These blank spaces are called "Stiffeners". Generally they are present in the blisters to avoid bending of the blisters.
After forming or sealing the PVC or PVDC sheets tends to get shrink which leads to bending and it gets difficult to place them in Cartons. So, stiffeners are provided so as to avoid the bending.
After forming or sealing the PVC or PVDC sheets tends to get shrink which leads to bending and it gets difficult to place them in Cartons. So, stiffeners are provided so as to avoid the bending.