First, to prevent the bottle later use deformation.
The main reason is to ensure that the product filling, as well as later transportation, use process will not cause the bottle convex bottom deformation due to internal pressure. Such as the design of the concave pentagon, so that it can be moderately deformed to reduce the degree of damage.
Second, material savings.
If it is made into a flat bottom, due to the pressure of the liquid, the bottom must be thickened, resulting in a waste of material, and the use of concave, from the surface is a waste of material, can increase the ability of the liquid pressure, so that the bottom is thinner but saves the material.
Third, increase the strength of the bottom of the bottle.
The Pet material itself is very smooth, in order to increase the grip of the bottle when placed, it will not slide or tip easily.