Why Are There Dimples in the Bottom of Milk Jugs?

Whether you buy whole milk, 2%, or skim, the plastic containers it comes in all share something in common. There’s a dimple built into one side of the jug where a smooth, flat plane would normally be. If you drink milk, you’ve probably seen this, but you may not know the ingenious reason behind the design. It turns out to provide structural integrity. A full gallon of milk with flat, rigid sides may be fine sitting in your refrigerator, but if you were to drop it on the floor, it would likely rupture. The dimple can prevent that from happening. When a jug hits the ground, the dimple warps outward and gives the milk a place to go when it expands on impact. Incorporating some wiggle room into the design makes the container more flexible and, therefore, more durable. That feature also comes in handy as the milk approaches its expiration date. Milk contains harmful microbes that expel gases over time. As these gases accumulate, pressure in the jug builds, and the flexible dimple again stops the jug from exploding.