text: Thermal insulation of a building refers to the walls, windows, and doors (anything exposed to the outside elements and atmosphere), and their ability to restrict the passage of heat from the inside out or outside in.  All materials are measured in terms of R value, or thermal resistance.  When calculating the amount of heat allowed to transmit through a wall, window, door, or other building component, the formula to use is Q=UA(Toutside - Tinside) where\n\nQ= the amount of heat transfered expressed in Btus/hr\nU=thermal conductance of building component that the heat is trying to pass through, also U = 1/R\nA= surface area of wall that makes up that component\nToutside = outside air temperature\nTinside = inside air temperature\n\nEach different type of material or component has different abilities to restrict the flow of heat.  Mainly it is due to the amount of air within the component (air within a building wall is a bad transmitter).  What insulation trys to do is break up the wall into numerous small air pockets.  Heat has to first raise the temperature of the first pocket before it can heat up the pocket next to it.  This occurs over and over until there is not enough heat to keep heating up air pockets.  Fiberglass insulation has millions of these air pockets and therefor makes a great insulator.  Stone (brick) or metal on the other hand has none so after you heat up the material, the heat then can begin to heat up the next thing to it, probably the atmosphere.\n\nSo a material with a high R value restricts the flow of heat more than that of one that has a low R value.  Window, since they are normally made up of one or two panels of glass typically are the highest point of heat loss/gain within a structure.  The worst types are the ones constructed of just a single pane of glass.  More high efficient ones are made of glass that has a greater propensity to heat up, and also have a vacum between two panes of glass.  \n\nThere are many types of thermal insulating products available.  See the attached website for a short list.  Mainly the walls are constructed with rolled-insulation (R-19 where the number denotes the R value) up to R-38 rolled-in insulation.  There are sprayed-in the wall cavity insulations where the R-value can be as high as 48.  \n\nThe main type of insulation is not just the insulation, but the type of construction of the wall.  Wall constructed of plywood over 2x4's with rolled in insulation have a lower thermal insulating value than those with Brick over plywood over 2x6's since you can put more insulation within the 2x6 cavity.  As you can see, the type of wall is also very important.