Why There’s a Dent in Your Milk Jug—and What It Actually Does

Why the Dent Pops In or Out

Ever notice how the dent changes shape? That’s the jug’s pressure control mechanism at work:

• When cold, the dent pulls inward.
• When warm, it pushes outward.

This design prevents the jug from bulging or collapsing — the same principle that keeps soda bottles intact, only safer and smarter.