When considering interior protective packaging for products which must 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 the package can be expected to encounter in its 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 which are 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 products surfaces under varying conditions (i.e., temperature, humidity, etc.). However, 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.


Industry-Wide Standards Required

In order to consider void fill in a performance-related manner, the industry should establish a common definition of the term in a way which will enable us to deal with it in the appropriate context. However, there is not yet such a standard, so for this purpose, we might think of our objective in using void fill as maintaining the interior array and original interior packaging orientation within the shipping container.


Consider that void fill (both the material and the process) is most often associated with container-sized consolidation efforts. In these cases, an effort is made 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 very 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 cases such as these, 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.


In these instances, our description of the objective of void fill to maintain an original interior array of products or interior-packaging orientation perhaps becomes more applicable. In fact, it is an almost intuitive action for even a non-packaging professional to judge the effectiveness of a package by picking it up and shaking it to see if it rattles indicating that the contents are loose and unsecured inside. The utilization of void fill should eliminate the rattle.


Take Your Pick

Perhaps because of the lack of standards for this area, or for any number of other reasons, there has been an impressive variety of different products promoted over the years for use as void fill. There have been any number of different 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 that we have used successfully over the 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.


Know Your Environment

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 the 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.


This discussion relates to applications where the materials or forms of interest are only to be used as void fill. In fact, in many cases, the package design will require a combination of cushioning and void fill, or any void fill form being considered would also have to provide some level of surface protection (or at least not have a negative effect on the product surfaces). In these instances, the process of package design or development will also include consideration of these factors in addition to void fill performance.


Factors such as these, along with weight (or density) of fill, ease of fill, speed of packaging, inventory space requirements, cost per unit, disposal and reuse considerations and customer acceptance, all should be taken into consideration, but only after each form has been subjected to the same verification test procedures we would apply to any new package design. Testing in accordance with a standard, such as ISTA Procedure 3A, should be an integral part of any new package verification, even if only to verify the specific void fill options.


William Armstrong is the Immediate Past President of International Safe Transit Association (ISTA) and is currently the Technical Development Manager at Sealed Air Corporation. He can be reached at 203-791-3625, bill.armstrong@sealedair.com or www.sealedair.com. For more information on ISTA, please visit www.ista.org or call