It’s possible that you haven’t spent much time pondering the design of milk jugs, but there are those who wonder why they have circular dimples on their sides. The circles built into milk jugs provide several benefits, but the specific reason for them has nothing to do with milk. They actually allow the jug to flex slightly, rather than keeping a solid, rigid shape. This is super important if you ever happen to accidentally drop a gallon of milk. Rather than cracking or shattering, the semi-flexible plastic used to make the jug — along with the indented design — allows the jug to take a harder hit. That’s because the indentations provide a place for the jug to expand outward when the pressure spikes. It’s still possible to drop milk jugs hard enough to break them open, but the circular dimples prevent this from happening most of the time. That’s not the only benefit of the circles. During the milk’s shelf life, some harmless bacteria produce gas inside the closed jug. The indentations allow the jug to expand slightly to accommodate the extra air, which is why you sometimes see the indentations poking outward.
