Here's why:

* Iron oxide: Rust is primarily iron oxide (Fe₂O₃). Iron itself is a decent conductor of heat.

* Porosity: Rust is porous, meaning it has many tiny air pockets. Air is a very poor conductor of heat.

* Overall: While the iron in rust conducts heat to some degree, the porous nature of rust and the presence of air significantly reduce its overall thermal conductivity.

Compared to other materials: Rust is a much poorer conductor of heat than metals like copper, aluminum, or even plain iron. It's closer to the thermal conductivity of materials like wood or plastic.

Practical implications:

* While rust won't be a major issue in most situations involving heat transfer, it can still have some effects. For example, if you have a rusty metal pan, it might heat up unevenly or take longer to cook.

* In some cases, the poor thermal conductivity of rust can actually be beneficial. For example, rust can help to insulate metal surfaces, preventing them from getting too hot or cold.

In summary, rust is a conductor of heat, but its thermal conductivity is relatively low due to its porous structure.