Most people don’t pay attention to the small circular dent on the side of a plastic milk jug, but it actually serves several important functions. This dent isn’t there for decoration or by mistake — it’s an intentional design feature that helps the jug manage pressure, stay strong during transport, reduce plastic usage, and make recycling easier. When the jug is filled, the liquid inside creates pressure.

The dent works like a flex point that can expand or contract slightly to prevent the jug from cracking or becoming misshapen, especially during stacking or when temperatures change. It also allows the jug to absorb some impact if dropped, which helps prevent spills or breakage.