Spray Polyurethane Foam - Pros and Cons

One great advance in insulation technology is spray polyurethane foam (SPF). With a Polyurethane made from two highly toxic chemicals: methylene diphenyl diisocyanate, and a Resin also known as the polyol blend, and is comprised mostly of polyols, with smaller amounts of catalysts, blowing agents, flame retardants and surfactants. 

Spray polyurethane foam, commonly referred to as SPF, is a spray-applied insulating foam plastic that is installed as a liquid and then expands many times its original size. It offers excellent insulating properties, improving energy efficiency in commercial and residential buildings, and is also used in many specialty applications.

Although there is a STYROFOAM™ Brand Spray Polyurethane Foam (SPF), these types of spray foams come in all types for all purposes. There use and handling is very dangerous, so I would never call them "green", however they can be used properly to create a very solid insulation barrier, that will last for decades (if not centuries) and create a vapor and moisture barrier that can save energy and thus indirectly save the environment. 
Spray Foam has some great advantages...

• Very High R-Value for size
• Easily sprayed into tight spots
• Can be very water resistant
• Increases the strength of the existing walls
• Excellent vapor retarder, creates a good barrier
• Good sound control by filling cracks and crevices
• Highly durable

Unfortunately, there are also many drawbacks to be overcome ...

• Looses its ability to insulate over the years
• Breaks down at 250-degrees, like all plastic
• Can give off toxic fumes, off-gassing
• More expensive than traditional materials
• Use fossil fuels in production
• Greenhouse gases are produced by the blowing agents
• Fumes can be deadly if inhaled, Installers of polyurethane foam need to be protected when applying the foam to a project
• Some people have allergies to the foam, and If this type of foam comes in contact with the eyes, they should be rinsed thoroughly and attended to immediately because temporary blindness can occur.
• Very difficult to do any remodel or make changes after foam is sprayed.
• Lasts forever, so how do you dispose of it when the building's life-span is done?

Remember Polyurethane Foam is made from molecules that are not found in nature. Here is one great alternative that you might want to use: Ecovative Design's - Greensulate (TM)