Building insulation materials are the building materials which form the thermal envelope of a building or otherwise reduce heat transfer. Insulation may be categorized by its composition (natural or synthetic materials), form (batts, blankets, loose-fill, spray foam, and panels), structural contribution (insulating concrete forms, structured panels, and straw bales), functional mode (conductive, radiative, convective), resistance to heat transfer, environmental impacts, and more. Sometimes a thermally reflective surface called a radiant barrier is added to a material to reduce the transfer of heat through radiation as well as conduction. The choice of which material or combination of materials is used depends on a wide variety of factors. Some insulation materials have health risks, some so significant the materials are no longer allowed to be used but remain in use in some older buildings such as asbestos fibers and urea. Consideration of materials used Factors affecting the type and amount of insulation to use in a building include: Thermal conductivity Moisture sensitivity Compressive strength Ease of installation Durability – resistance to degradation from compression, moisture, decomposition, etc. Ease of replacement at end of life Cost effectiveness Toxicity Flammability Environmental impact and sustainability Considerations regarding building and climate: The average climate conditions in the geographical area the building is located The temperature the building is used at Often a combination of materials is used to achieve an optimum solution and there are products which combine different types of insulation into a single form. Spray foam Spray foam is a type of insulation that is sprayed in place through a gun. Polyurethane and isocyanate foams are applied as a two-component mixture that comes together at the tip of a gun, and forms an expanding foam. Cementitious foam is applied in a similar manner but does not expand. Spray foam insulation is sprayed onto concrete slabs, into wall cavities of an unfinished wall, against the interior side of sheathing, or through holes drilled in sheathing or drywall into the wall cavity of a finished wall. Advantages Blocks airflow by expanding & sealing off leaks, gaps and penetrations. (This can also keep out bugs or other vermin) Can serve as a semi-permeable vapor barrier with a better permeability rating than plastic sheeting vapor barriers and consequently reduce the buildup of moisture, which can cause mold growth. Can fill wall cavities in finished walls without tearing the walls apart (as required with batts). Works well in tight