INSULATION (THERMAL) is a material used to inhibit heat transfer.  More simply, insulation keeps-in heat when it's cold outside, or keeps-out heat when it's hot outside.  It's used in buildings, vehicles and boats.  It's used in roofs, walls, floors and around pipes to keep them from freezing or losing heat in hot water.  Insulation is a value contributor with good return on investment by lowering heating and cooling costs.  It is also an environmental plus by reducing the energy needed to maintain comfortable temperatures where humans and animals spend time.

Thermal insulation used in construction comes in several shapes and products. The most common form is rolls of fiberglass known as batting.  These rolls are rolled out and placed between studs in exterior walls, between rafters and trusses in attics with no floor, or between joists in attics or on first floors where the underside is exposed to the outside (e.g., crawl spaces).  Another common form of insulation is blow-in or sprayed-in material that conforms to the area applied.  The common products include cellulose, which is treated paper, shredded polystyrene, loose fiberglass and denim. Styrofoam panels are another common insulating material.

Batts (batting sheets) are sections of insulation attached to paper or foil that allows them to be laid between joist or rafters in a way where the paper or foil is used to fix the batt to rafter.  Rolls of insulation (e.g., fiberglass) also will be attached to liner medium (paper or foil) and can be cut into length (batts) by the installer.

Loose insulation is best applied with an insulation blower. Loose insulation, such as cellulose, is normally treated for flame resistance, while fiberglass is naturally flame resistant.  Blown-in insulation typically comes compressed in bags. These require the material to be appropriately expanded for optimum benefit.  For cellulose and fiberglass, this expansion is easily done using an insulation blower with a 100 foot hose.  Because power is not always available and the use of a blower is not always convenient, raked insulation is also available.     

The effectiveness of thermal insulation increases by the thickness of the layer of insulation.  The following table shows the per inch increase in R Value of different materials.  The R-value in insulation refers to the material's thermal resistance or its ability to resist the flow of heat. It measures how effectively an insulation material can prevent heat from passing through it. The higher the R-value, the greater the material's insulating effectiveness.

R-value is an essential metric used to assess and compare the thermal performance of different types of insulation. It helps determine the appropriate type and thickness of insulation needed in buildings to achieve desired energy efficiency and comfort levels.

Building codes and standards often specify minimum R-values for insulation in various parts of a structure, such as walls, roofs, floors, and ceilings. The recommended R-value depends on factors like climate, local regulations, and the desired level of energy efficiency.

Different insulation materials have varying R-values per inch of thickness. For instance, fiberglass, cellulose, foam board, spray foam, and other types of insulation materials have different R-values. Combining insulation materials or increasing the thickness of the insulation can improve the overall R-value of the building envelope, reducing heat transfer and improving energy efficiency.

It's important to note that while R-value is a critical factor in assessing insulation performance, other factors like installation quality, air sealing, moisture resistance, and building design also play significant roles in the overall energy efficiency and effectiveness of insulation in a structure.