Basic principle. Air becomes lighter when it is heated. When the temperature of the air in the balloon is sufficiently above that of the outside air the balloon will rise. A hot air balloon comprises an envelope, basket, and burner. The average sport balloon has a volume of approximately 2,000 cubic metres and weighs around 200 kilograms. Buoyancy can be reduced by partially releasing air via a vent at the top. Typical equipment consists of an altimeter, variometer, GPS, UHF and Airband radios.

The envelope is the technical name for the colourful part of the balloon. Other than the heat-resistant fabric for the aperture at the lower end, balloons are made of synthetic fibres such as nylon and polyester. These fabrics are treated with a very thin heat retaining coating to stop the air escaping. The envelope is shaped rather like an inverted light bulb, which allows the greatest buoyancy for the smallest surface area. The air inside the envelope reaches 100 degrees Celsius or more during flight. When fully inflated it holds its shape by internal pressure which is so strong that it would be possible to walk on the top of the balloon.

The burner is the engine of the balloon. It is not on continuously, being switched on for longer periods when ascending and shorter periods when descending. The basket typically carries up to four 20 kilogram tanks of liquid propane gas, enabling a flight of 2-3 hours.

The basket is made of wicker (cane) because it best absorbs the shock and stresses which can occur in landing. A basket for a balloon carrying three or four people is about one metre deep, 1.2 metres wide, and one metre high.

How do you steer? A balloon drifts with the wind. Usually the wind direction changes with height thus allowing an experienced pilot to control the direction of flight quite accurately by either ascending or descending. A GPS unit is often used to give an instantaneous reading of wind direction and strength.

Airworthiness. Balloons must be inspected for airworthiness every year or every 100 hours of flight time. Many factors impact the service life such as the type of fabric, maintenance and conditions under which it is flown. Generally, envelopes with more than 500 hours are considered old but may still be airworthy if properly maintained. New balloons cost around $50,000 fully set up, with some special shapes costing upwards of $100,000. A decent secondhand balloon can cost around $20,000, but good advice is needed before buying one.

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