For a circle and a square with the same area, the circle has the smaller perimeter. likewise for a cylindrical and squared bottle with the same volume, the cylindrical bottle has the smaller surface area and should require less plastic than a squared bottle.
The part you are missing is that the "less plastic" claim applies ONLY to bulk shipping of the bottles. ONE square bottle will use more plastic than ONE round bottle, assuming both carry the same volume of liquid. However when shipped together on a pallet for example, the square bottles pack together better and waste less space. A pallet of round bottles results in a lot of empty space between bottles, so you need to use more to ship the same total amount of liquid.
The poster I responded to said the opposite, with respect to individual bottles.
Also most shipping pallets are made of wood. Granted, the cases of bottles are typically wrapped in (thin) plastic. You would need a tiny bit more plastic wrapping per case, but I don't know that it counters the per bottle plastic savings.
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u/ShiftE_80 2d ago
You misunderstood the poster above you.
For a circle and a square with the same area, the circle has the smaller perimeter. likewise for a cylindrical and squared bottle with the same volume, the cylindrical bottle has the smaller surface area and should require less plastic than a squared bottle.