The concept of a functional barrier
Safe Packaging Design - Principles, Modeling and Foundations

The concept of a functional barrier is central to U.S. (FDA) and European (EU Regulation No. 10/2011) regulations. It allows for the granting of exemptions: a recycled material or a controversial additive may be used, provided that a demonstrated functional barrier limits actual migration below regulatory thresholds.

There is no formal, official definition of functional barriers beyond the idea of “a layer that prevents migration.” Here, we propose two operational definitions based on total release potentials ($PR$) (equation (21)) and partial (equation