flight. Turning vents help a pilot align the basket for landing,  or in the case of commercial balloons, align the balloon’s  logo toward the crowd. the generic illustrations ,  and are also listed in the glossary  which contains balloon and aeronautical terminology. Some  terms and names used by manufacturers are also included.  The envelope is usually made of light-weight and strong  synthetic fabrics such as ripstop nylon or Dacron$^{®}$. The  material is cut into panels which are sewn together in vertical  rows that are called gores due to their triangular shape.  The traditional envelope shape is a teardrop. The gores  are reinforced with sewn-in webbing called horizontal and  vertical structural load tapes which are continuous to the  top center of the balloon where they are sewn into a load  ring. Galvanized, stainless steel, or Kevlar$^{®}$ cables transfer  basket loads to load tapes which in turn support the load.  The nylon “skirt” at the base of the envelope is coated with  special fire resistant material to keep the flame from igniting  the balloon.  Balloons that do not have a traditional “teardrop” shape are  called special shape balloons.  [Figure 2-5] They may be  completely engineered systems which have been designed to  resemble cans, sports balls, cartoon characters, cars, etc.  The deflation port is located at the top of the envelope and  allows for the controlled release of hot air. It is covered by  the deflation panel sometimes called a top cap, parachute  top, or spring top.  [Figure 2-4]  In a balloon with a parachute  top, partial opening of the parachute valve is the normal way  to cool the balloon. Balloons with other types of deflation  panels may have a cooling vent in the side or the top. Many  balloons are also equipped with turning vents, which allow  for the pilot to turn the balloon on its vertical axis while in  Some balloons have appendages added to the envelope.  Appendages are pieces added to a balloon envelope in order  to create a particular shape or rendition, not necessarily  keeping with a standard shape balloon. To be designated  an appendaged envelope, less than 10 percent of the total  capacity of the balloon is contained within the appendage.  While the appendaged envelope has the same general flight  characteristics as a standard balloon shape, there are some  differences. For example, the added weight of the appendage  may cause the overall envelope to weigh significantly more  than teardrop balloons of equal size. Appendage balloons  also have the tendency to rotate during aggressive climbs  and descents.  A special shape envelope requires a substantial amount of  engineering to ensure the envelope is properly stressed,  and the balloon has no undesirable flight characteristics  due to the shape. Special shape balloons built in the United  States or the United Kingdom are normally issued Standard  Airworthiness Certificates, but special shape balloons  imported from other manufacturers in other countries may  be issued an Experimental Airworthiness Certificate. A  balloon with an Experimental Airworthiness Certificate  usually may not be flown for compensation or hire, which  negates the marketability of such a balloon. Additionally, an  experimental balloon may not be flown over congested areas,  Special Shape Balloons Envelope  2-4 Figure 2-4.  Deflation system. Figure 2-5.  Special shape balloons. Overlap for air seal Actuation line  (deflation/vent)