What is perforation in printing?

Perforations do two opposite jobs at once. They have to survive everything that happens to the pack before the customer touches it — die-cutting, gluing, packing, a courier network — and then give way easily and in a straight line when someone pulls. Those requirements pull against each other, which is why the cut-to-tie ratio is specified rather than left to chance.

A coarse perforation with long cuts and short ties tears very easily but weakens the sheet, and can open in transit. A fine perforation with short cuts and long ties is robust but tears raggedly, and on heavier board may not tear at all without a start point. Most production work sits between the two, and the sensible way to settle it is on the sample rather than on paper.

Common uses in packaging include tear-open strips on mailers and shipper cases, tamper evidence on carton flaps, detachable coupons and vouchers, and the tear tape on a taped pharmaceutical outsert. On commercial print, perforation is what lets a reply slip come off a leaflet without scissors.

On the dieline, perforation lines are drawn on their own layer and conventionally shown dotted, because they become a separate perforating rule in the steel die.