Flights from one point to another within the same country are called domestic flights. Flights from a point in one country to a point within a different country are known as international flights. For modern sport balloons the envelope is generally made from nylon fabric and the inlet of the balloon (closest to the burner flame) is made from fire resistant material such as Nomex. Beginning during the mid-1970s, balloon envelopes have been made in all kinds of shapes, such as rocket ships and the shapes of various commercial products, though the traditional shape remains popular for most non-commercial, and many commercial, applications. A hot air balloon for manned flight uses a single-layered, fabric gas bag (lifting "envelope"), with an opening at the bottom called the mouth or throat. Blimps are the most commonly built airships because they are relatively easy to build and easy to transport once deflated. However, because of their unstable hull, their size is limited. There is a wide variety of types differing in the construction of their wings, aerodynamic efficiency, location of the pilot, controls and intended purpose. However, modern technology gives pilots the ability to soar for hours, gain thousands of metres of altitude in thermal updrafts, perform aerobatics, and glide cross-country for hundreds of kilometres.
