Spray foam insulation is an alternative to using fiberglass insulation batts (pre-cut panels of insulation that comes in various length, widths, and R-values) or fiberglass insulation rolls (insulation that comes in 93-inch rolls of various widths and R-values that you cut to size) and is applied with a pressure sprayer. There are two types of spray foam insulation: open-cell foam and closed-cell foam. The tiny cells in open-cell foam are open, and air fills the spaces between the open cells. The tiny cells in closed-cell foam are closed and filled with an inert gas. Open-cell foam is lighter and less expensive than closed-cell foam, but closed-cell foam has better insulating properties than open-cell foam. One of the main advantages of spray foam insulation is that it is good for adding insulation to existing finished areas, irregularly shaped areas, and around obstructions. In new construction, spray foam insulation can add strength to a building's structure. The trade-sponsored web site SprayFoam.com provides a great deal of information about spray foam insulation and also provides a searchable database of spray foam installation contractors in the United States, Canada, and Europe.

http://www.sprayfoam.com/