If it can't end up in your food... do you really need to worry about FDA compliance?

What is a Functional Barrier?

In a recent StepLadder article, we discussed the definition of a "food additive:"

  • Any substance the intended use of which results or may reasonably be expected to result — directly or indirectly — in its becoming a component [of] or otherwise affecting the characteristic of any food.1

Components of food packaging may or may not, therefore, be considered "food additives" (thereby subject to premarket approval by FDA), depending on their intended use. So how do we address substances that aren't intended to contact food at all because they're used behind some type of barrier layer or material?

Common examples of barriers, in the lay sense, include: a polyethylene layer placed between paper and food to impart moisture-proofing properties, or a bag of chips that has an aluminum foil liner that separates the chips from the outer layers of the bag (which could be made of plastic, paper, or even additional layers of foil). If a manufacturer reasonably believes that a barrier layer should prevent migration of substances from the outer layer(s) of the packaging to food, is that enough to conclude that they don't need to evaluate those substances for FDA compliance? Not necessarily!

The term "functional barrier" is a legal term of art by which a component of packaging completely prevents migration of a packaging material to food. A barrier layer is not necessarily a "functional barrier" just because packaging is physically separated from food by an intervening layer, however. In fact, only one of the two examples described above might actually constitute a functional barrier! (Hint: it's the aluminum foil). Very few materials are considered to be functional barriers under all temperature Conditions of Use and in contact with all Food Types. For the rest, the presence or absence of a true functional barrier is necessarily evaluated on a case-by-case basis. Companies should consider additional factors, such as:

  1. The molecular weight of the potential migrant(s)
  2. The nature and thickness of the intervening layer(s)
  3. Time and temperature conditions of contact
  4. Types of food placed in contact with the packaging material

Although FDA does recognize the concept of a functional barrier, it hasn't provided much guidance to industry on the subject. The term "functional barrier" is not specifically defined in the Federal Food, Drug, and Cosmetic Act. We do, however, find certain examples of "functional barriers" in FDA's food additive regulations and in various sources of guidance. For example, 21 C.F.R. § 177.1390(a) ("Laminate structures for use at temperatures of 250°F and above") of the food additive regulations states that aluminum foil may properly be considered a functional barrier in laminate structures used at high temperatures.2 FDA also describes functional barriers (sometimes referred to as "effective barriers" or just "barriers") in its recycled plastics guidance3 and in its chemistry recommendations4 for preparing premarket submissions for food contact substances. These include layers of polyethylene terephthalate (PET): (1) at a thickness of ≥ 25 micrometers (μm) (0.001 in) at room temperature and below; and (2) at a thickness ≥ 50 μm (0.002 in) at higher temperatures.5

While common sense says that thicker layers of many types of materials are more likely to serve as effective barriers to the migration of components of food packaging to food, certain materials are more effective than others. Further, certain materials may serve as effective barriers at lower temperatures, but become less so at higher temperatures. The central theme throughout each of the regulatory references cited above is that a true functional barrier must be demonstrated (e.g., through modeling or analytical testing) to actually prevent migration of substances from packaging when used as intended. While the examples described above are by no means an exclusive list of materials that may be considered functional barriers, companies that intend to rely on the concept of a functional barrier are responsible for demonstrating that migration of the component of food packaging to food is precluded.


1. See Section 201(s) of the Federal Food, Drug and Cosmetic Act.

2. Metallic deposition layers are not necessarily considered such barriers, and foil layers with pinhole defects are not considered functional barriers.

3. FDA, Guidance for Industry: Use of Recycled Plastics in Food Packaging (Chemistry Considerations) (July 2021), available at: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/guidance-industry-use-recycled-plastics-food-packaging-chemistry-considerations.

4. FDA, Guidance for Industry: Preparation of Premarket Submissions for Food Contact Substances (Chemistry Recommendations), December 2007, available at: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/guidance-industry-preparation-premarket-submissions-food-contact-substances-chemistry

5. See also Baner, A., Brandsch, J., Franz, R., and Piringer, O. 1996. "The Application of a Predictive Migration Model for Evaluating the Compliance of Plastic Materials with European Food Regulations," Food Additives and Contaminants, 13 (5), pp. 587-601.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.