Conduction, convection and radiation are the three methods of heat transfer. As gases or liquids are heated, they warm, expand and rise after losing density. As they cool, they get denser and fall, creating a convection current. Conduction occurs when materials are in direct contact with each other.
The three methods of heat transfer all transfer heat in different ways. Conduction heat transfer involves the transferring of heat through solid objects. Convection heat transfer is the transfer of heat through liquid or gas. Radiation is known as the transfer of heat, in electromagnetic energy form, through space.
The idea of insulation is to slow heat transfer in a conditioned environment. During cold or hot weather, insulation is used to keep heat inside or out of a home, room or building. In both hot and cold climates, it is important that houses and buildings are properly insulated from the outside elements. In temperature-controlled homes or buildings, insulation can save on energy costs. All types of insulation has an "R-value" which is a number that indicates an amount of conductive heat transfer that a material can resist. Insulation with a high R-value is considered to be very resistant to heat transfer.
An example of conduction is when the inside of a wall in a particular house or building becomes cooler as a result of cold temperatures or conditions on the outside of the wall. An example of convection would be cold air entering a room full of warm air resulting in a lowering of the room's overall temperature. Radiation heat transfer occurs when sunlight enters a room that is air-conditioned through a single-paned window, resulting in an slight warming of the overall temperature of a room.
Metals are considered to be one of the most efficient conductors of thermal energy. Conductivity of materials decreases as density decreases which is why liquids and gasses are traditionally less conductive than solids. The earth is warmed by the sun through electromagnetic wave radiation.