What is Air Pillow? Most of the time, the outer carton is larger than the product you need to pack. The empty space around the product is called a 'void'. Filling these voids will help you prevent movement of the product within the carton box. Void fill air pillow bags is a great way to protect and cushion your product from vibration damage. Why use air pillow for void filling? Air Pillow Bags can make you add exactly what you need to fill void areas within the box, while protecting your products.