Before we look at insulation we must see how thermal energy moves. There are three ways it moves. The first is by conduction. Conduction is the transfer of energy by direct contact of particles. Heat spreads through out an object till the object is the same all the way around. (Physical Science section 6.1, page 1)
This happens because all particles vibrate unless in an absolute zero situation. These more violently moving particles hit each other. Eventually these particles will vibrate at the same speed. Conduction takes place in all the states of matter. Solids conduct heat better then liquids or gases because the particles are more tightly packed. Solids, such as metals are good conductors of heat. Insulators are not good conductors of heat. (Physical Science section 6.1, page 1)
The second way thermal energy travels is through convection. This is the transfer of thermal energy through the bulk movement of matter. This only happens in liquids and gases. As a gas or liquid gets lighter it expands and thus is less dense. It then rises and you get currents. This is how there are ocean currents and air currents(Physical Science section 6.1, page 1).
The third way is by radiation. This is the transfer of thermal energy through waves. This radiant energy is given of in waves by one object and is absorbed by another and changes into thermal energy. Lighter colors reflect radiant energy while dark colors absorb it. All objects that are warmer then absolute zero emit radiant energy. (Physical Science section 6.1, page 1 and 2)
Insulation does not allow heat to travel through it easily. This is why they are not good conductors of heat. Insulation uses trapped air pockets to make it hard for heat to flow through. There are three basic types of insulation: fibrous, cellular, and granular insulation.
Fibrous insulation is made up of tiny diameter fibers which finely divide the air space. The fibers can be perpendicular or horizontal to the object being insulated. They may not be, however, bonded together. Silca, rock wool, and alumina silca fibers are used. The most common and widely used are fiber glass and mineral wool insulation. (Swales)
Cellular insulation is composed of small individual cells of air completely divided from each other. The cellular material that may be used are glass or foamed plastic such as polystyrene, polyurethane, and elastomeric. (NIA)
Granular insulation is composed of little nodules which contain hollow spaces. It is not considered to be a true cellular material because gas can be transferred into the spaces. This can be produces as a lose or pourable material that is used in attics in between the beams and not on the walls. It can also be mixed with binders and fibers to make a more rigid insulation. A few examples of these are calcium silicate, expanded vermiculite, perlite, cellulose, diatomaceous earth and expanded polystyrene.(NIA)
There is a rating system for insulation. A piece of insulation is given an R-value. This gives an idea of how well it keeps thermal energy from flowing through. An R-value needs to be higher in the ceiling, like 30 to 44, because heat rises and that were it is most likely to escape. A one pane sheet of glass has a R-value of one. A two paned window filled with air in between has a much higher R-value. Fill the space in between the same window with argon, the R-value goes remarkably higher then it was before. (Physical Science section 6.1, page 2)
http://www.insulation.org/insulation. NIA (National Insulation Association)