Air slowly diffuses through regular latex balloons, but the gaps between latex molecules are small enough that it takes a long time for enough air to leak out to really matter. If you put helium into a latex balloon, it diffuses out so quickly your balloon would deflate in next to no time.

Why does air go out of a balloon?

The collision of these air particles with the walls creates a high-pressure environment inside the balloon relative to the atmospheric pressure around it. This is why when a balloon is released, the high-pressure air flows out of the balloon to the low-pressure air surrounding it: "Winds blow from high to low."

How do you stop balloons from deflating?

Store the balloons in a large plastic bag until the time for the party. This will help prevent the balloons from deflating. Tie the bottom of the plastic bag shut with the balloons inside.