The shell carries load
Curved regions help the continuous base manage pressure-related loads without treating the bottom as a simple flat panel.
Episode V084 · Source record
Why Soda Bottles Have Five Feet
Many carbonated PET bottles use a petaloid base because the bottom must resist pressure-related deformation while still making stable contact with a flat surface. The feet, valleys, center, material distribution, and molding process work as one system.
- Research lock
- August 12, 2026
- Evidence stack
- 8 source records · 8 direct links
- Visual proof
- Three creator-owned PET specimens
ONE SELECTED CARBONATED PET BOTTLE
CURVED BASE. FIVE CONTACT FEET.
FIVE IS COMMON · NOT MANDATORY
The sourced answer
The base solves a pressure problem and a standing problem at the same time.
The feet define contact
Projecting feet provide defined contact regions on a flat surface while the center and valleys remain recessed.
The count can vary
Five is common in documented examples, but other counts and base families exist. The complete geometry matters more than one number.
Original specimen proof
Real bases establish the geometry. Original diagrams explain the mechanism.
The carbonated specimen shows five projecting feet and recessed valleys. The still-water specimen and juice-bottle specimen show visibly different segmented bases. Those comparisons establish variation without turning one bottle into a category rule.
Creator-owned or permission-cleared specimens. No artificial pressure test.
- H1 is a selected carbonated-beverage PET bottle with five feet
- W1 has three primary lobes, each divided into three molded panels
- J1 has five major lobes, each divided into two molded panels
- Panel seams are not counted as separate contact feet
- Public derivatives remove location, device, audio, and camera metadata
The mechanism graphics are original, vendor-neutral explanations. They reproduce no patent drawing, supplier render, academic figure, brand, label, or trade dress.
The complete system
The visible feet are only one part of the engineering.
Material distribution
Stretch history and wall-thickness distribution affect the finished base, so more plastic in one place is not a complete design rule.
Valley and center behavior
Valleys and the central region remain structural parts of one shell and can be important in rollout or stress-cracking analysis.
Production handling
Foot contact, conveying, pallet stability, temperature, and use conditions add constraints beyond pressure resistance alone.
Direct source library
Trace every public claim.
Each note states what its reference supports and where the evidence stops. External sources open in a new tab.
Pressure and standing
The base must resist pressure and still define a standing plane
These patent records document pressure-loaded petaloid bases, unwanted base deflection, projecting feet, recessed valleys, and variation in foot count.
S01Locked 2026-08-12
US20160144992A1
Google Patents record of a U.S. patent application
The record describes carbonated-beverage pressure, projecting feet separated by valleys, and foot apexes that can define a standing plane. It is a design record, not a universal specification.
S02Locked 2026-08-12
US9580206B2
Google Patents record of a U.S. patent
The patent documents outward center deflection and positional instability as design problems. The episode treats them as risks, not inevitable failures for every bottle.
S03Locked 2026-08-12
EP2555984B1
Google Patents record of a European patent
This record documents a curved base with five hollow foot formations and also a seven-foot variant. Its count preference belongs to that invention and is not a universal rule.
Material and manufacturing
Valleys, wall distribution, and stretch history affect the result
The academic and supplier records support a bounded discussion of valley stress, stretch blow molding, material distribution, rollout, conveying, and pallet stability.
S04Locked 2026-08-12
Bottom Design of Carbonated Soft Drink PET Bottles
Journal of Applied Polymer Science via SeoulTech
The peer-reviewed study found the highest maximum principal stress at a valley in the design it analyzed and reported improved crack resistance after redesign. That stress map is study-specific.
S05Locked 2026-08-12
Experimental and Computer Simulation of Stretch Blow Molding
Polymer (Korea) via SeoulTech
The research record supports stretch blowing from a preform and treating thickness and stretch-ratio distributions as measurable design variables. It does not establish one universal production recipe.
S06Locked 2026-08-12
StarLITE Tropical
Sidel
The supplier describes wall distribution, stress-cracking resistance, base-rollout resistance, foot contact, conveying, and pallet stability as interacting goals for its own CSD base system.
Variation
Different package requirements can produce different base families
These current manufacturer records support the limited comparison among pressure-resistant, hot-fill, and other PET bottle designs while preserving the selected-specimen boundary.
S07Locked 2026-08-12
PET Bottle
Toyo Seikan
The manufacturer describes biaxial stretch blow molding and distinguishes pressure-resistant carbonated bottles from hot-fill and pressure-plus-heat-resistant categories. It is a manufacturer taxonomy, not a global standard.
S08Locked 2026-08-12
Why Does the Bottom of a Carbonated Drink Bottle Have Five Feet?
Suntory customer information
This current manufacturer example describes five petal-like feet for pressure resistance and self-standing behavior. It supports one documented bottle family, not a rule for every bottle.