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Cake day: March 28th, 2024

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  • Believe it or not, @themeatbridge@lemmy.world is correct, just not about why. It’s to adjust for differences in jug size caused by temperature.

    Plastic jugs are made by blow molding, where a tube of plastic is warmed, then inflated within a mold using compressed air to create its shape. In winter, the air and environment are cooler so the plastic is also cooler and accordingly a bit less elastic while getting blown. This results in jugs that contract a bit more while cooling and are a bit smaller. To compensate, cool weather jugs have a shallower dimple. The alternative is either warming the air or warming the molds more, both of which cost more, while this actually slightly saves money by using a bit less plastic. The converse is true for summer jugs - bigger dimple, warmer air - as the warmer plastic molds more easily.

    The dimple also adds a bit of structural stability, so the jugs can be made of slightly thinner plastic. These factories pump out millions of jugs, so even a $0.005 saving per jug adds up.

    I actually did some work for a company that makes plastic containers, so I got it straight from them. Otherwise I’d provide a source. What I could find online that corroborates is low quality local reporting, so I didn’t bother with URLs.