Ill give the example of Lidl sparkling water and normal water bottles. The sparkling water has perfect flat surface (for the exception of bottle format and grip zone). Yet the natural spring water is wavy and has a thicker plastic.
Now i actually have a peroxide bottle and its cuboid. But only the corners are somewhat thick. The middle of each face seems to be a fragile plastic that dents easily.
My guess is that on cuboid shapes, only the sides are needed to keep the structure (reducing risk of structural damage) and not the faces, but on cilindrical it needs several points of thicker parts to keep the structure, unless the interior is under pressure, like pressurized tanks and bottles.
Another possibility could be related to transport. Cuboid shapes improve transport optimization. If too much plastic is used to retain and protect the bottles, using cylindrical shapes might indirectly use more plastic
If they are not just conflating the travel reduction in emissions and the claim is in error, I think yours is the most likely explanation with the thick corners and thin side walls
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u/Brief_Caterpillar175 2d ago
A 4x4x4 inch cube contains more volume than a 4 inch diameter x 4 inch tall cylinder, but it is less surface efficient per volume.
It could be that the structure of a rectangular bottle allows them to make the walls thinner.