What is the envelope of a hot air balloon made of?

The envelope of a hot air balloon is typically made from lightweight, durable materials such as ripstop nylon or polyester. These fabrics are often coated with a heat-resistant material to withstand the high temperatures generated by the burner. The design of the envelope helps to trap hot air inside, providing the lift necessary for the balloon to ascend. Additionally, the seams are reinforced to ensure safety and structural integrity during flight.