Ever noticed the small round dent on the side of a milk jug? It’s not a design flaw or decoration—it actually serves a smart purpose.

That dent helps the jug adapt to pressure changes. Since milk expands and contracts with temperature shifts, the dent acts like a built-in stress ball, preventing the jug from cracking or bursting, especially if frozen.

It also functions as a shock absorber. If the jug is dropped or jostled, the dent redistributes impact to reduce the risk of cracks or spills—saving mess and money during transport.

Surprisingly, it also strengthens the jug while using less plastic. Like architectural arches or cardboard ridges, the dent adds structure without extra material, keeping the jug light yet durable.