Blonde Girl With Huge Breasts Strips Her Yellow Underwear In The Bed With Ballons

When you fill up a balloon with air, the balloon is being stretched. While the balloon is constantly releasing kinetic energy in an attempt to contract, it is also being pushed back out by the constant bouncing of the internal air molecules.
Basically, the internal air has to exert force not only to counteract the external air to keep the air pressures "even", but it also has to counteract the natural contraction of the balloon. Therefore, it requires more air pressure (more force) than the air outside the balloon wall.