Perhaps you missed this:

"When the pack is outfitted with the standard components, there is some extra room to add personal gear and to accommodate some of the options we expect some customers to select. The unused space is filled with ultralight 3/8-inch closed cell insulating foam that a survivor can use to insulate themselves from the cold ground; no sense wasting space. The pair of 24-inch long cinch straps that secure this foam roll can be used for shelter building or other survival purposes. If the customer prefers, they can dispense with the foam and save 3.1 ounces. The foam can be cut shorter with a utility knife or household scissors to fit a smaller space if the customer adds personal gear."