Air between windows is a thermal insulator.
One example of an element denser than air is sulfur hexafluoride (SF6). It is a colorless, odorless gas that is significantly denser than air, allowing it to be used in certain applications such as electrical insulation.
Electrical insulation
Voltages in that range do not use insulation around the conductor. They are bare conductors and use air and separation from one another for the insulation factor.
One can find low cost insulation installers by contacting the company of Air Seal Insulators Inc. The company uses Toronto spray foam insulation from quality producers like BASF and the material used produce the best results.
Insulating foam is just one thing that can be used. Insulating the wall cavity stops heat exchange with the exterior which is a problem during extreme climate conditions like winter and summer. Insulation works by stopping air movement through the cavity. The real trick of insulation is that it isn't the insulation material itself that stops the heat exchange, it is the air trapped in it that does. Air is a poor conducter of heat energy provided that the air is stagnant (not moving around). When applied, the foam bubbles up as it expands, trapping air in the bubbles as it hardens making it an excellent heat insulator by virtue of the air trapped in it.
Insulation and sheetrock are related only in the sense that they are used in walls. When one side is drywalled insulation batts can be stuffed in the other side and then boarded up.
An air lift pump is used to press down air. Most commonly used when allowing light to be drawn in when necessary. For example a fish tank will use one.
Yes, layers of insulation will offer better efficiency than one layer. This is because it keeps more heat out and keeps the cool air in.
Cross-Linked Polyethylene and Polyvinyl Chloride are a couple of insulating materials used for the insulation of electrical conductors. This type of insulation allows the wires an insulation factor of 90 degrees C.
A batt is one of a series of fibres used for stuffing, especially for insulation.
There is more than one kind of insulation, the main types being thermal and electrical. Fiber glass is commonly used for thermal insulation, and rubber is a good electrical insulator.
One can find information on thermal insulation from Insulate, Government site called Energywise, Energy Star, British Gas and Energy websites. Thermal insulation is used to reduce heat transfer from one object to the other.