Why do PET bottles have indented bottoms?
Short answer
A shaped base helps a bottle handle internal pressure, especially in carbonated drinks, while keeping the bottle stable on a surface.
How it works
Carbonated drinks create pressure inside a PET bottle. If a thin, flat base simply pushed outward under that pressure, the bottle could become unstable and tip over.
Many bottles use a rounded, petal-like base with supporting feet. This spreads the pressure and lets the outer feet keep the bottle upright. The exact base shape changes with the contents and manufacturing method.
Key point
The indentation is not only decorative. Bottle designers balance pressure resistance, stability, material use, and manufacturability when choosing the base shape.