Here's why:

* Solids have tightly packed molecules that vibrate and transfer energy very efficiently through conduction.

* Liquids have more freedom of movement, but their molecules are still close enough for efficient conduction.

* Gases have widely spaced molecules, making conduction much slower.

Heat transfer methods:

* Conduction: Heat is transferred through direct contact between molecules.

* Convection: Heat is transferred through the movement of fluids (liquids and gases).

* Radiation: Heat is transferred through electromagnetic waves.

While radiation can be very efficient, it's not the primary method of heat transfer within a material.