The statement suggests that the extensional viscosity values obtained from the CaBER (Capillary Breakup Extensional Rheometer) do not represent "true" rheological data. It is important to consider the context in which this statement is made, as it might be influenced by the specific experiment or materials involved.

The CaBER measures extensional viscosity based on a liquid filament's capillary thinning and breakup. While this provides a good approximation of extensional viscosity, it's true that the measurements can be influenced by a variety of factors, such as the material's viscoelastic properties, the initial filament diameter, the imposed strain rate, and the analysis methodology.

Furthermore, while extensional viscosity is an important parameter in rheology, it is not the only one. Shear viscosity, for instance, is also a crucial aspect of a material's rheological behaviour. Suppose the statement is in the context of needing a fuller rheological profile. In that case, it may be suggested that relying solely on CaBER-derived extensional viscosity is insufficient for a comprehensive understanding of the material's rheology.

Thus, the statement might mean that while the data from the CaBER is useful and provides some rheological information, it may not fully capture all the complex rheological behaviour of the material under investigation. It's always a good practice to use multiple techniques and measurements when characterizing the rheological behaviour of materials to ensure a more comprehensive understanding.

As you noted, a capillary rheometer is indeed capable of measuring several different types of rheological data. Using a combination of measurements, such as shear viscosity, extensional viscosity, and extrudate swell, will likely yield a more comprehensive rheological profile of the material.

Dear Dr. Joshua Depiver,

Thank you very much for your detailed explanation. Put the statement in its context and combine your comments. I understood that statement.