Do aerosol cans have to be cylindrical?They can be square, but it\'s a lot easier and cheaper to make round cans that can withstand the internal pressureSquare ones would need much thicker walls and/or reinforcingHow often do you see square balloons? Addendum: As a marketing gimmick, how can square cans be manufactured cheaplyish, that would hold the pressure? Well, let\'s see, one way is to consider a square can that has a square cross section, but has a bulge in the middle, so that all four sides are actually segments of a cylindrical surfaceProducing such cans out of seamless aluminum would be difficult, but not impossible, requiring entirely new tooling from the conventional ones that have been in use for over half a centuryAnother variant of this idea is to have wavy sides, while maintaining a square cross section, so that at least most of the surface area is composed of segments of a cylindrical surfaceWith a little refinement, it should be possible to keep the flexure of the can from internal pressure to a minimumThis, again, would be even harder to manufacture than the previous idea, but not impossibleif a large beer company was willing to spend millions in developing tooling for such unusual aluminum cans, it can be doneSuch a wavy can with square cross section might be able to be refined to the point where it\'s almost like a vertical box, but nonetheless, having that small amount of waviness is critical to its structural strengthAddendum 2: You know, I recall that years ago I used to fold a piece of paper that could be rolled together into a slender vertical box with wavy sidesNow that I think about it, maybe that can be done with tin cans, and I believe it could be structurally sound for internal pressures.Other related question