Here's why:

* Permeability: Different materials have different permeabilities. This means some materials allow gases to pass through more easily than others. For example, a balloon is permeable to helium, but not to air.

* Size and Shape of Molecules: Gases are made up of molecules that have a specific size and shape. Some materials have pores or gaps that are too small for gas molecules to pass through.

* Pressure and Temperature: The pressure and temperature of a gas can influence its ability to permeate a material. Higher pressure and temperature can increase the rate of permeation.

Examples:

* A balloon: A balloon is made of a material that is permeable to helium, allowing it to inflate. However, it is not permeable to air, so the balloon will eventually deflate.

* A glass of water: While some gases can dissolve in water, the glass itself is not permeable to gases.

* A brick wall: Brick walls are designed to be impermeable to gases, providing insulation and protection.

Conclusion:

While some materials are more permeable to gases than others, no material is completely permeable to all gases. The ability of a gas to pass through a material depends on various factors, including the material's properties, the gas's properties, and the surrounding environment.