Spray Foam Insulation

Among  the many materials used for insulation, spray foam  is relatively new, with some of the most commonly used products today having come to the market in the mid-1980's . Spray foam insulation is made of synthetic materials, usually poylurethane or latex foam. Polyurethane, a kind of plastic, was invented during World War 2 and used in aircraft. 
Spray foam is actually the product of the chemical reaction between two liquids. The liquids are held separate and mixed before they are applied with a special machine that heats them up and presses them through two hoses that meet at the tip to combine them, then applied to the  area to be insulated. Spray foam insulation goes onto the surface wet and expands as it dries and hardens with a rough surface. Spray foam insulation needs to applied with skill because it expands beyond where drywall extends which causes it to need to be skillfully scrapped so the drywall sits correctly. The most common name-brand spray foam insulation product is called "Icynene". 

There are two kinds of spray foam insulation open cell and closed cell. Cell refers to the bubbles that comprise to the foam. Open cell foam is made of cells that are not completely closed off, the cells having openings. These kind of bubbles admit more air, this kind of foam is more pliable and supple, giving the spray foam kind of a spongy texture. Open cell foam insulation is also less dense than closed cell foam, sometimes up to four times less. It also has about half the r-value  of closed cell spray foam  (r-value is the measure of a material's ability to prevent heat flow). One of the major advantages of open cell insulation is that it can reach very narrow areas like cracks and fissures because it is more flexible. Open cell foam is also best for soundproofing because it is better at absorbing the energy transmitted from the air outside the insulation to the air inside the insulation due to it's more open structure. Open cell foam  is also generally less expensive than closed cell insulation. 

Closed cell  foam denotes foam where the bubbles that comprise it are completely sealed off from one another with practically no breaks, with the cells tightly compressed together. Closed cell foam is about four times as dense as open cell foam. Usually closed cell foam is is made of chemicals rather than water and an insulating material like with open cell insulation. Closed cell foam is stronger than open cell, harder and less flexible. Because of its density, it is also has more material per given volume and more costly. For this extra cost, closed cell generally has a higher r-value than open cell foam. Closed cell foam's rigidity allows it to add to the structural strength of a building (for this reason it is almost always the kind of sprayfoam used underneath a roof). Closed cell foam is a good a blocking moisture vapor and is more or less impervious to water.