Why Milk Jugs Have That Circular Dent

It Helps Handle Pressure Changes

One of the main reasons milk jugs have that circular dent is to manage pressure.

Milk containers go through temperature changes during filling, transportation, refrigeration, and storage. As temperatures shift, the air and liquid inside the jug expand and contract. Without flexibility in the plastic, the container could warp, crack, or even burst.

The circular indentation acts like a pressure-release zone. It allows the plastic to flex inward or outward slightly when pressure changes occur, helping the jug maintain its shape.