It is important to understand heat and its properties in order to control it or contain it.
Temperature is an objective measurement of kinetic energy. Kinetic energy is the movement energy of an object. On a microscopic level, a material or system of molecules, atoms, electrons and particles are always moving and vibrating. Simplistically, the more rapid this movement, the more kinetic energy and the higher the temperature of the material. Potential energy of the system is how the molecules are arranged. If the molecules are tightly and orderly arranged, the system can pass kinetic energy through the system efficiently. This kinetic and potential energy is known as thermal energy and the transfer of this energy is heat.
Thermal energy can be transferred (heat or heat transfer) in three different ways: conduction, convection and radiation.
Conduction is the flow of energy from a region with high temperature to a region of low temperature. It is the rate of the flow of energy, not the amount of energy. Pots and pans are made of metals that are good conductors. The molecules are organized and are high in potential energy. When a flame is introduced to one side of a pan, it doesn’t take long for the other side to feel hot. It moves the energy through the system quickly and efficiently.
Convection is the circular motion that happens when warmer gas or liquid rises and displaces cooler gas or liquid. This occurs because the warmer the system, the faster the molecules are moving and the less dense the system is. The molecules in cooler systems are not moving very fast and are closer together, so they are denser and gravity pulls them down. Think of a rolling boil in a saucepan or a weather pattern of warm air colliding with cold air creating wind.
Radiation is the transfer of heat by means of electromagnetic waves. All objects radiate energy in the form of electromagnetic waves, the higher the temperature of the object, the more it radiates. Objects at room temperature radiate energy as infrared waves. Hotter objects (more energy) increase the frequency of the wave and shorten the wavelength into the spectrum we can see—Red, Orange, Yellow, Green, Blue, Indigo, Violet, before once again undetectable by humans with microwaves. This is best demonstrated with a flame. A blue flame is hotter than an orange flame, and the blue flame is closer to the reaction (the source of energy) than the orange flame.
Now that we understand a little bit about what is going on at the molecular level, we can be more effective in keeping heat inside a system like a furnace or range or keeping it outside of a system like a refrigerator or an air conditioner. All of this points to different insulating materials, how they work and how they can be designed and fabricated to the maximum efficacy.