After the balloon envelope is laid out, a gas-powered fan forces unheated air through the balloons mouth, filling the fabric and giving the pilot space to light the balloon’s burners. This is called cold inflation. After the envelope is filled, the balloon is stood-up by igniting the burners and heating up the air inside. That’s called hot inflation. After the envelope is over the basket, and the pilot checks his equipment, the passengers are allowed to board.