Balloon canopies are generally constructed from long nylon gores, each having a basic sinusoidal shape. Seams are reinforced with sewn-in webbing - particularly for larger balloons. Each gore, extending from the base opening of the envelope to the crown, may consist of a number of smaller panels. This basic construction is often clearly defined by the various colours of the fabric.
In most cases, the canopy is created using lightweight ripstop nylon, a material that is strong and relatively heat resistant. The gauge of the nylon may range between 0.75 and 2.2 ounces, with several different gauges used in a single balloon. The material closest to the burners, around the opening at the base of the canopy, and for the scoop, may be coated with fire-resistant chemicals. Nomex is a special fire-resistant material used for this purpose.
One cubic foot of air weighs approximately 36 grams, (0.0807 lbs or about 1.29 ounces) at standard temperature and pressure. However, when the temperature of a cubic foot of air is increased by 100 Farenheit degrees, perhaps from room temperature to 120 degrees Farenheit, its weight decreases by about 7 grams. Consequently, each cubic foot of air contained in the envelope of a hot-air balloon has the potential to lift about 7 grams. A model balloon with a capacity, for example, of 2,500 cubic feet can therefore theoretically lift 2,500 x 7 grams - ie 17.5 kilograms. In practice, not all the air contained in a balloon envelope is maintained at the same temperature, so the calculation becomes rather more complicated. It is also important to remember that the canopy itself has significant weight even before a basket or gondola and other equipment is added.