A spine of a digipak is the fold of the digipak with about the same thickness of the tray. A lot of people ask why the inside spine cannot have artwork printed on it. The answer is actually yes and no. Yes in the sense that you can still print artwork on it but the printing cost will almost double. For that reason a lot of people choose to leave the spine blank.
The following video explains why.
If for the sake of continuity of your artwork you need to print the inside spine please ask our sales representative about it.