The Code of Federal Regulations states, "a food shall be deemed to be misbranded if its container is so made, formed, or filled as to be misleading." More specifically, "a container that does not allow the consumer to fully view its contents shall be considered to be filled as to be misleading if it contains nonfunctional slack-fill." Slack-fill is the difference between the actual capacity of a container and the volume of product contained therein. Nonfunctional slack-fill is the empty space in a package that is filled to less than its capacity for reasons other than the six categories listed below.
So, consider this example of strawberry jam... the consumer can fully view the contents of this package. There is no need to worry about slack-fill here. Even if this package was taller, but contained the same amount of jam, the package would not be misleading as the reasonable consumer can see the product contained in the package.
But, let’s consider another example - 3oz of ground black pepper in a 4oz tin. Seems fine, right? Actually, no - this is potentially misleading - The difference becomes apparent when we put the 3oz of pepper in a clear 4oz box. This is non-functional slack-fill and it is why we need to be cautious when designing our packaging.
There are only six categories that can be defined as "functional" slack-fill. These are:
Protection of the contents of the package;
The requirements of the machines used for enclosing the contents in such package;
Unavoidable product settling during shipping and handling;
The need for the package to perform a specific function (e.g., where packaging plays a role in the preparation or consumption of a food), where such function is inherent to the nature of the food and is clearly communicated to consumers;
The fact that the product consists of a food packaged in a reusable container where the container is part of the presentation of the food and has value which is both significant in proportion to the value of the product and independent of its function to hold the food, e.g., a gift product consisting of a food or foods combined with a container that is intended for further use after the food is consumed; or durable commemorative or promotional packages; or
The inability to increase the level of fill or to further reduce the size of the package (e.g., where some minimum package size is necessary to accommodate required food labeling (excluding any vignettes or other nonmandatory designs or label information), discourage pilfering, facilitate handling, or accommodate tamper-resistant devices).
There are cases where non-functional slack-fill is present, yet the brand owners have made good efforts to depict the product on the package. There are also cases of marginal slack-fill where brands may have inadvertently used packaging or print to veil the difference in volume, resulting in a lawsuit.
There is not a clear methodology of assessing slack-fill. There is also not a published threshold of acceptable amounts of non-functional slack-fill. As a packaging professional, you need to be cautious of non-functional slack-fill - it’s simply not permitted.
Slack-fill is a growing concern - you can check out our Packaging Regulations course to view additional slack-fill packaging cases: https://www.packagingschool.com/courses/packaging-regulations-101