Package cushioning is used to help protect fragile items during shipment. It is common for a transport package to be dropped, kicked, and impacted: These events may produce potentially damaging shocks. Transportation vibration from conveyors, trucks, railroads, or aircraft can also damage some items. Shock and vibration are controlled by cushioning so that the chance of product damage is greatly reduced. Cushioning is usually inside a shipping container such as a corrugated box. It is designed to deform or crush to help keep levels of shock and vibration below levels that may damage the product inside the box. Depending on the specific situation, package cushioning can often be between 50 and 75 millimeters (two to three inches) thick. Internal packaging materials (sometimes the same ones used for cushioning) are also used for functions other than cushioning. Some are used just to immobilize the products in the box and to block them in place. Others are just used to fill a void and do not have a cushioning function.