We'd thought about using polystyrene boxes taped together, but didn't like the environmental impact of using that type of material en-masse, or the amount of storage they would take up compared to card boxes which are recycleable and flat pack.
We also thought that having a box that was made for 4 mugs looked more professional as product packaging, than 4 polystyrene boxes taped together.
This is the 4 way Listawood box, they also have a 6 way version...
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Mugs slot in nicely, and don't need extra padding.
http://www.listawoodtradesupplies.com/i ... GPA&pgnum=