Why is milk box rectangular and soft drink can cylindrical?

I happened to stumble upon an interesting book a few days ago. I can't remember what the title is, but it's a book about economics, something about why economists can answer some interesting facts of life. Written on the cover is some quirky questions like the one in the title. So, why are milk boxes rectangular rather than cylindrical, like soft drink cans? The answer, it seems, is also a bit quirky. First of all, science has proven that cylindrical cans can withstand much higher pressure than its rectangular counterpart. Soft drinks are mostly carbonated drinks, hence they exert higher pressure than standard liquid. If soft drink cans were rectangular in shape, I doubt you will be able to drink it after you pull of the ring. Another explaination is the user-friendliness. Soft drinks as we know are meant to drink immediately after opened, so it is more rational to be in cylindrical shape. Imagine holding a rectangular shaped soft drink can. It will be hard to get a grip onto the can. And think about this: if soft drink cans were in rectangular shape, then Arnold would not be able to squeeze it open with only one hand, would he? Then came the economic-esque explaination. Economists say that cylindrical shape wastes much more space than rectangular one, if they are to put on shelf. Soft drinks are stored in whatever places you can imagine: on the shelf, inside your cupboard or even your closet, on top of the fridge, on your coffee table during CNY, in shooting range, by the roadside, etc etc. There's no need to worry about space. On the other hand, milk is not as cincai as soft drinks. Milk has to be stored in refrigerated shelf, which means the running cost is higher. So, instead of wasting space making them into cylindrical shape, companies have came up with the idea of packing them in boxes. This design fully uses up all available space on the shelf, so it's much worth the cost of storing them. Something the economists call the cost-benefit factor. There you go, the reasons why milk is in boxes while soft drinks are in cans. Well, that's what I remember. Not exactly what the book says, but almost. I will continue reading it if I happen to walk by the bookstore again (yes, I was reading it inside the bookstore, for FREE!). Coming up next: Why is soft drink can tall and slim rather than short and wide (both have the same volume), even though making the can short and wide saves about 30% of aluminium?