Why do my folded business cards crack at the seam?
Also, choose a stock (card) variety that has tightly bonded fibers, because the paper surface can pull away from the body when folded. This increases the chances of cracking. Keep in mind that thinner paper cracks more easily than thicker ones.
And don’t think that UV coating or press varnish would stop the seams from cracking, either. In fact, cracking is less likely to be seen if there is no ink or coating on the fold.
What you can do is apply laminate to cover the surface of the paper and keep it from cracking. Scoring, where you create a crease in the card where the fold line will be placed, could also minimize the likelihood of cracks.