The bottom of the plastic bottle is concave

(1) The simplicity of the bottle making process - due to the concave shape of the five corners of the bottom of the bottle, the blowing is simpler (the specific reason is that it is the trade secret of the Coca-Cola Company, we have no way of knowing it).
(2) Material saving - If the flat bottom is made, the bottom must be thickened due to the pressure of the liquid, resulting in waste of materials. The use of a concave shape is a waste of material on the surface, but in fact it distributes the liquid pressure evenly due to the five corners, which makes the bottom thinner and saves material.
(3) Increasing the strength of the bottom of the bottle - the concave design of the pentagonal shape allows it to reduce the degree of damage by moderate deformation.