A hot air balloon conit of a bag called the envelope that i capable of containing heated air. Supended beneath i a gondola or wicker baket (in ome long-ditance or high-altitude balloon, a capule),which carrie paenger and (uually) a ource of heat, in mot cae an open flame. The heated air inide the envelope make it buoyant ince it ha a lower denity than the relatively cold air outide the envelope. A with all aircraft, hot air balloon cannot fly beyond the atmophere. Unlike ga balloon,the envelope doe not have to be ealed at the bottom ince the air near the bottom of the envelope i at the ame preure a the air urrounding. For modern port balloon, the envelope i generally made from nylon fabric and the inlet of the balloon (cloet to the burner flame) i made from fire reitant material uch a Nomex.
Beginning during the mid-1970, balloon envelope have been made in all kind of hape, uch a rocket hip and the hape of variou.
commercial product, though the traditional hape remain popular for mot non-commercial, and many commercial, application.