What does mrfredrickson use up to fly his house?

In the film "Up," Carl Fredricksen uses thousands of colorful helium balloons to lift his house into the sky. He ties the balloons to the house and, with the help of his adventure spirit, sets off on a journey to fulfill a promise to his late wife, Ellie. The balloons symbolize hope, adventure, and the desire to hold on to cherished memories.