What Are “Shell” Dice?
Shell dice are dice that contain an unnumbered die inside the numbered shell exterior. The purpose of the shell is to protect the interior die’s design. This can further expand the customization of the dice set to include specific imagery, or color combos that wouldn’t normally be as clean or as possible if a standard method was used. In addition, the shell will protect the design from fading, getting scratched, or other effects that the set will go through during its rolling lifetime. The interior die will not affect rolling because both the interior and exterior are made of the same material and therefore have the same density all around the die.
As these sets require hand painting designs and a second round of sanding, this is also why they are at a higher price point than the standard sets also featured on the AsseT Dungeoneering site.