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Some types of insulation require professional installation, and others you can install yourself. You should consider the several forms of insulation available, their R-values, and the thickness needed. The type of insulation you use will be determined by the nature of the spaces in the house that you plan to insulate.
Batts are flexible products made from mineral fibers, including fiberglass or rock wool. They are available in widths suited to standard spacings of wall studs. When installing batts, make sure they fill the entire wall cavity, and that there are no gaps or squishes which would significantly decrease the effectiveness of the batt. They must be hand-cut and trimmed to fit wherever the joist spacing is non-standard (such as near windows, doors, or corners), or where there are obstructions in the walls (such as wires, electrical outlet boxes, or pipes).
Blown-in loose-fill insulation includes cellulose, fiberglass, or rock wool in the form of loose fibers or fiber pellets that are blown using pneumatic equipment, usually by professional installers. This form of insulation is typically installed in unfinished attic floors. Cellulose is made from recycled newspapers and is treated with a fire retardant.
In the open wall cavities of a new or exposed wall, cellulose and fiberglass fibers can also be sprayed after mixing the fibers with an adhesive or foam to make them resistant to settling.
Foam insulation can be applied by a professional using special equipment to meter, mix, and spray the foam into place. Polyicynene is an open-celled foam. Polyisocyanurate and polyurethane are closed-cell foams. In general, open-celled foam allows water vapor to move through the material more easily than closed-cell foam. However, open-celled foams usually have a lower R-value for a given thickness compared to closed-cell foams. So, some of the closed-cell foams are able to provide a greater R-value where space is limited. Foams are usually installed along attic rooflines and in areas where space is limited.
Rigid insulation is made from fibrous materials or plastic foams and is produced in board-like forms and molded pipe coverings. These provide full coverage with few heat loss paths and are often able to provide a greater R-value where space is limited. Such boards may be faced with a reflective foil that reduces heat flow when next to an air space. Rigid insulation is often used for foundations and as an insulative wall sheathing. Rigid insulation should also be installed on vertical and sloped walls in the attic.
Reflective insulation, also called a radiant barrier, is a metallic foil material (usually aluminum) designed to block radiant heat transfer across open spaces. Reflective insulation is most effective at reducing cooling bills in hot, sunny climates. However, in some cases (special installations) the product can help reduce heating bills as well. Keep in mind, the effective (calculated) R-value of the product will vary depending on the direction of heat flow (up, down, sideways). The performance and long-term cost-effectiveness of the product depends on number of factors, including where the product is installed, how the product is installed, and the amount of existing insulation currently in the home. The U.S. Department of Energy and the Florida Solar Energy Center (FSEC) have excellent and detailed web sites that explain how the product works, general guidance on the best way to install the product, which climates the product is most cost effective, and energy savings that can be expected.
Source: Department of Energy – Insulation Fact Sheet
 How and Where Insulation Should Be Installed
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