The present invention presents an air bag, and a method of using the same, which has at least one indicator line marking thereon for providing a visual indication of when the air bag is in a properly inflated condition for filling a void between loads, such as cargo or the like, in a truck, airplane, train or the like. Each indicator line includes a center portion which is of a first design, such as being blue-colored, and having easily identifiable ends. Preferably, each indicator line has end portions of a second design, such as being red-colored, which are on opposite sides of the center portion of the line and which are visually distinct from the first design. The center portion of the indicator line has a length which is substantially equal to the maximum thickness of the air bag. The air bag is properly inflated when the end portions of the line are not visible, or the center portion of the line marking is completely visible between the loads and the junctions between the center portion and the end portions of the line marking are just visible between the loads. When inflated to the latter, the air bag is also inflated to its maximum pressure. In a second embodiment, the indicator lines extend vertically from the top seam to the bottom seam of the air bag. The air bag is properly inflated when the inner edges of the lines are visible between the loads.