A unit load device (ULD) is a container used to load luggage, freight, and mail on wide-body aircraft and specific narrow-body aircraft. It allows preloading of cargo, confidence the containerised load will fit in the aircraft and efficient planning of aircraft weight and balance and reduced labour and time in loading aircraft holds compared with 'bulk-loading' single items of cargo or luggage by hand. Each ULD has its own packing list or manifest so that its contents can be tracked. A loaded aircraft cargo pallet secured with a cargo net also forms a ULD, but its load must be gauged for size in addition to being weighed to ensure aircraft door and hold clearances. The IATA publishes ULD regulations and notes there are 900,000 in service worth more than US$1 billion, averaging $ each. Types ULDs come in two forms: pallets and containers. ULD pallets are rugged sheets of aluminium with rims designed to lock onto cargo net lugs. ULD containers, also known as cans and pods, are closed containers made of aluminium or a combination of aluminium (frame) and Lexan (walls), which, depending on the nature of the goods to be transported, may have built-in refrigeration units. Examples of common ULDs and their specifics are listed below. Notes Aircraft compatibility LD3s, LD6s, and LD11s will fit 787s, 777s, 747s, MD-11s, Il-86s, Il-96s, L-1011s and all Airbus wide-bodies. The 767 uses the smaller LD2s and LD8s because of its narrower fuselage. The less common LD1 is designed specifically for the 747, but LD3s are more commonly used in its place because of ubiquity (they have the same floor dimensions such that one LD3 takes the place of one LD1). LD3s with reduced height ( instead of ) can also be loaded on the Airbus A320 family. LD7 pallets will fit 787s, 777s, 747s, late model 767s (with larger doors), and Airbus wide-bodies. Interchangeability of certain ULDs between LD3/6/11 aircraft and LD2/8 aircraft is possible when cargo needs to be quickly transferred to a connecting flight. Both LD2s and LD8s can be loaded in LD3/6/11 aircraft, but at the cost of using internal volume inefficiently (33 ft3 wasted per LD2). Only the LD3 of the LD3/6/11 family of ULDs can be loaded in a 767; it will occupy an entire row where two LD2s or one LD8 would otherwise have fit (90 ft3 wasted per LD3). Policies vary from airline to