The function and design of PET container bases

You may perhaps have noticed that PET bottles have a wide variety of different bases? Some of them stand on “footlets”, others are quite flat, and others again have a “ribbed base”. But why exactly is this the case?

Function and design – mutually exclusive?

Every design is influenced by both functional and aesthetic considerations. In some cases, the shape will be the primary focus, while in others the purpose is paramount. The sentence “Form follows function” coined by the American architect Louis Sullivan is frequently cited – unfortunately, though, this precept is often misunderstood. Actually, you see, Sullivan was not postulating the primacy of function over aesthetics, but stating that the appearance of objects has a function in itself. So a good designer has to decide in each and every case which aspect is more important: the form or the function.

When it comes to the base of a PET bottle, this is not a particularly difficult decision. Since the base is crucial to container’s technical performance, and is therefore one of the most important functional sections, it’s no accident that it looks the way it does. Here, at least, the primary focus is definitely on functionality.

The base geometry is selected to suit the type of product involved. This is why the base of a bottle for still water looks different from that of a bottle for carbonated water. But why is this necessary?

In the case of carbonated beverages, in contrast to still products, the PET bottle is under internal pressure, i.e. the base has to be able to withstand this internal pressure without being deformed. After all, the container is required to stand upright on the conveyor inside the line, and not least on the supermarket shelf as well. Stabilising ribs in the areas between the “footlets” keep the base stable, by overall and ideally forming a hemisphere.

In the case of packages for still water, for example, or for aseptically bottled beverages like dairy products or juices, there will be no (or almost no) internal pressure, thanks to a nitrogen droppler in the bottle. That’s why this base looks significantly flatter.

But how do our clients choose their bases?

Well – often our clients will in fact have a more or less specific idea of what they wish their bottle to look like. Many of them want what is called a “champagne” base, because of its upmarket character and its resemblance to glass bottles.

Unfortunately, however, most of these bases are less than ideal for the technical requirements the containers have to meet. They require a large amount of material for the stability needed, which increases the weight of the package, often “unroll” under internal pressure, and are more difficult to manufacture.

In order to nevertheless meet our clients’ wishes in terms of their design or particular technical requirements, Krones has for a good decade now been developing a variety of different base geometries. For example, we have developed the first free-form base (Carbo Classic Base*) of its kind.

As can be easily imagined, due to the abundance of different bases that by now exist, it’s not been easy for our clients, nor for our intern staff either, to keep abreast of all the variants involved.

We took this consideration on board, and last year launched a workshop with a team chosen for interdisciplinary specialisms, tasked with creating a harmonised nomenclature for the bases.

This workshop was chaired by Arno Haner and Timo Janssen – I asked them and Jochen Forsthövel a few questions on this subject

Arno, what were the aims and motivation behind creating a nomenclature for PET bottle bases?

Harmonised names quite generally improve communication and mutual comprehension, which helps to preclude error potentials, mix-ups, etc. What’s more, we approach our clients with a coherently comprehensible naming system.

How long did it take until the names had been finalised?

This development process involved numerous requirements, like innovation, clarity (not least in an international context), a clearly comprehensible structure or other stipulations relevant to marketing. Despite all these requirements, we managed to finalise the nomenclature within a few short months in some cross-departmental workshops. 

Timo, how does this designation system work?

The system consists basically of tripartite terms. The first part answers the question of the application category involved. The second describes a typical characteristic of the base. Third part: well yes, inevitably “base” ….

Jochen, one final word, please, on the subject of bases?

Bases – often overlooked, but the section of the bottle that has to incorporate the most know-how. Thus, by marrying outstanding design to technical expertise in an aesthetically appealing form, we are able to offer ideal solutions to our clients.

And if you want to know now why the Carbo Classic Base* is a true classic then you still have to be patient for a little while: in my next articles I’ll be dealing in more detail with the various kinds of base encountered. 🙂