Helium balloons work because helium is less dense than air. This means that a balloon filled with helium will be lighter than the same balloon filled with air. The difference in density creates a buoyant force that pushes the balloon up.

The amount of lift a balloon generates depends on the difference in density between the helium and the air. The greater the difference in density, the more lift the balloon will generate. This is why balloons filled with helium rise faster than balloons filled with air.

The density of helium is about 0.1786 grams per liter, while the density of air is about 1.29 grams per liter. This means that a balloon filled with helium is about 7 times less dense than a balloon filled with air.

The lift generated by a balloon can be calculated using the following formula:

```

Lift = (Density of air - Density of helium) * Volume of balloon

```

For example, a balloon with a volume of 1 liter filled with helium will generate a lift of about 1.11 grams. This is enough lift to lift a small toy or a few pieces of candy.

Helium balloons are often used for parties and other festive occasions because they are fun and easy to use. They can also be used for scientific experiments, such as measuring the density of different gases.