Protect Your Product: The art and science of void fill

Interior protective packaging helps products survive shipment from their point of manufacture to their ultimate point of use, we generally consider that these protective materials or systems will be designed to perform one or more of the following functions: cushioning, surface protection and void fill. Of these three, void fill is the least established in terms of any generally accepted performance-related metrics. In fact, there is no industry-wide definition for the term void fill.

Cushioning and surface protection, on the other hand, are standard throughout the industry. Cushioning is used to protect a packaged item from the various shocks, impacts, and vibrations during normal shipping or distribution environment. The basic function of cushioning is to mitigate these externally generated physical hazards to levels below those which will cause the products inside the package to be damaged. There are a number of industry accepted processes to not only confirm these capabilities in any specific package (i.e., ISTA Test Procedures), but to also create performance data for the available materials and systems that can be used to predict anticipated performance in a package before the design is accomplished.

Surface protection materials and systems can also be characterized as serving performance functions through procedures such as vibration testing of the finished package. There are also surface compatibility procedures for determining the degree to which a packaging material might be expected to react with a product’s surfaces under varying conditions (i.e., temperature, humidity, etc.). There are no industry-accepted processes for measuring void fill effectiveness or to establish the degree to which various void fill materials or systems can be expected to perform.

However, there is not yet such a standard, so for this purpose, we used to maintain the interior array and original interior packaging orientation within the shipping container, void fill—both both the material and the process—is most often associated with container-sized consolidation efforts. In these cases, to reduce the number of available standard container sizes to a minimum in order to maximize inventory efficiencies and to take advantage of quantity pricing on the number of container sizes being purchased for stock. This is a common practice in distribution center packaging operations or in applications where a large number of different size and weight shipments are made from a common shipping area.

The outcome of this practice is that a majority of product shipments are made in containers which are larger than would be necessary if only fit and protection requirements were considered. In these cases, it is seldom a good idea to ignore the extra space within the packages; instead, some sort of void fill materials or techniques are most often used.

Perhaps because of the lack of standards for this area, , there has been an impressive variety of different products promoted over the years for use as void fill. These include paper-based forms (wadded, embossed, crumpled, bogus, printed, unprinted, shredded, slit and expanded); expanded polystyrene (peanuts, donuts, stars, saucers, chips, chunks, noodles); wood (shredded and chipped); various plastic foams and forms; popcorn (real, grown-in-the-field, air-popped popcorn); inflated air pillows; and just about anything else which can be stuffed, shoved, poured, expanded, wrapped and packed into an empty space. Trying to compare the relative capabilities of these diverse forms for their use as void fill has been a fair challenge.

At Sealed Air, we have developed one such process over the past years: void fill efficiency. In this approach, a known amount of the material being evaluated is placed evenly in a rigid rectangular box of known dimensions (typically 12″ x 12″ x 18″ or 18″ x 18″ x 24″). The material is placed in the box in the same manner in which it would be placed in a package – layered, stuffed, poured, etc. A nominal 0.10 PSI top load is placed carefully on the material and the assembly is then vibrated for 60 seconds at 1 G and 5 Hertz. The volume occupied by the material under load after vibration is then used to calculate the void fill efficiency for that form. Typically, this value is expressed in pounds per cubic foot, square feet per cubic foot, cells per cubic foot or whatever the most appropriate quantity of measurement might be for that particular form. These values can then be used to estimate the quantity of each material that would be required to fill a given void space in a specific package.

The major fault with this approach is that not all void spaces need to be filled to provide adequate void fill performance. If our definition of void fill is to preserve the original array and interior-packaging orientation, then in many instances, this can be accomplished by appropriate placement of the material in the void rather than simply filling up all spaces. There are materials and forms where all spaces must be filled to accomplish our objectives (i.e., “flowable” products), but other forms, such as inflated air cells, can often accomplish the same performance objectives while not necessarily filling every nook and cranny of the package.

It is worth noting that various void fill materials and forms will respond in different ways to various typical distribution environment elements. Many will “settle” under distribution vehicle vibration conditions. Some will expand at reduced atmospheric pressures experienced at high altitudes. Some will be affected by exposure to hot and/or cold temperatures. Many earlier forms are subject to mold or other infestations resulting from high humidity and outdoor exposure. Some forms will degrade (dust, fragment, etc.) when exposed to impact and vibration. Many will change their occupied volume when subjected to impact or time under load (dynamic compression and compressive creep). So comparisons between various candidate materials can be a fair challenge, or at least more than just cost per cubic foot.

William R. Armstrong is technical development manager for Elmwood Park, NJ-based Sealed Air Corp., a protective packaging provider.

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