Why do my box folds crack and show white, and which paper helps?

Cracking usually appears where dark solids cross a fold: the ink and coating split and expose white fibre. Three fixes: use colour-through paper such as PALETTE (40 colours), whose colour belongs to the sheet so folds stay on colour; match the score to the grain direction and fold with the grain where possible; and keep heavy dark solids and hard UV off the fold line. Dry seasons make cracking worse, so condition paper to the pressroom before converting.