Pinholing is the formation of microscopic holes in flexible food packaging as the material flexes during handling, transport, and distribution, breaching the hermetic seal. Even invisible to the naked eye, pinholes admit oxygen and microorganisms, destroying the modified atmosphere or vacuum that preserves the product and leading to premature spoilage, rancidity, or blown packs. The defect plagues thin metallised films, foil laminates, and lightweight pouches, particularly at folds, seals, and creases where stress concentrates. Quality systems combat it through material specification, flex-crack resistance testing (the Gelbo test), careful handling protocols, and leak detection on lines. Pinholing illustrates a central packaging truth: barrier performance is only as good as the package’s weakest moment in the supply chain, not its laboratory specification.