Why do we use ping-pong balls?
To determine the interior space available to stash travel essentials, we’ve devised a range of measuring protocols. We use six beverage containers ranging in size and shape to gauge cupholder accommodation. We stack, stuff, and arrange 9-by-14-by-22-inch cardboard boxes to quantify the number of airline-carry-on-size suitcases that will fit in a trunk or folded seat’s cargo space. To measure irregularly shaped gloveboxes, door pockets, and console bins, we fill each container with 1.5-inch-diameter ping-pong balls. It’s tempting to convert the number of spheres to a volume (cubic inches), but we resist that calculation because—as with the box of tissues, 12-ounce can of soda, or gallon of milk you might stash in these compartments—there are voids between the balls. Random packing (our procedure) nullifies approximately one-third of the available space. The negative space between the balls could theoretically be reduced to 25 percent of an irregular shape with precise stacking, but while we might be pedantic, we’re not crazy.