Which of the following features is NOT required for liquid adhesives used on filters?

The feature that is not required for liquid adhesives used on filters is adhesive flexibility. In the context of adhesive application for filters, flexibility is not a critical characteristic. Filters often require adhesives that ensure a strong bond and can withstand environmental conditions, but high flexibility is not a necessary property since the adhesives primarily need to maintain the integrity of the bond under operational stress rather than to flex or stretch.

In contrast, other features such as high flash point are important to ensure safety during application, as a high flash point reduces the risk of fire. A lack of specific coating color allows for design flexibility in products using the filter, as colors may not significantly impact the performance or suitability of the adhesive with the filter material. Low viscosity is crucial for proper application, enabling the adhesive to spread evenly and penetrate the surfaces being bonded effectively. Thus, while flexibility can be beneficial in some applications, it is not a requirement for adhesives used in filter applications.