Some plastics wraps are permeable to gases (meaning they allow gases like air to pass through) while some others are not. Aluminum foil however, being a metal foil, has almost no permeability, meaning that no gas (air) can pass through. The reason why the plastic warp allows air though has to do with the structure of the plastic at the level of molecules (called polymers) from which the plastic is made up.

Aluminum foil, being an amorphous metal, would not allow air through. Plastic depends - some plastics are permeable to air, and some aren't. I don't know about plastic wrap that you use in the kitchen.