Question: How does Polyurethane Foam actually work?
Answer: Urethanes are plastics that have gas-filled bubbles that make them light weight and a good insulating material.
Question: What is the difference between open-cell and closed-cell polyurethane foams? 
Answer: These two types of polyurethane foams have different R-values, permeability, strength, and costs. Click here for more information
Question: What is the difference between CFC, HCFC and HFC blowing agents in polyurethane foams? 
Answer: These "Flouro-carbons" have different amounts of chlorine or are designed to prevent chlorine release into the atmosphere.
Question: Do urethanes "outgas" and are they toxic?
Answer: Urethanes are non-toxic and only require protection for our operators during installations, but the finished product is completely safe and has no formaldehydes.
Demelic had an independent testing laboratory test their HEATLOK product for off-gassing. They tested the product using the Underwriters Laboratory of Canada 705.1-98 test method. It is a pass/fail test, where the estimated indoor air concentration of volatile organic compounds is compared to the permissible concentrations. The permissible concentration is defined as 1% of the threshold limit value. The off-gassing for the HEATLOK product was under the permissible concentrations so they passed the test.
Question: Are urethanes good for sound insulation?
Answer:  Open-cell urethanes are better than closed-cell foams for reducing air-borne sound.  Both are good at sealing holes that can let sound through wall or ceiling penetrations.  Structure-borne sound CANNOT be controlled with low-density infill materials such as foam.
Question:  What sort of paint should I use for covering polyurethane foam?
Answer:  Typically, spray-applied polyurethane foam is covered by interior or exterior wall coverings or ceiling or roofing details. That said, on occasion it is left exposed and the concern really is only that of ultra-violet light that will degrade the exposed foam over time. In exterior applications, a paint will not suffice, rather a protective coating should be used. The Spray Polyurethane Foam Alliance provides an excellent resource for selecting the appropriate coating for your application, and we recommend that you visit their website for this information.
Question: I've been thinking that I can specify in our air barrier specification - products section, that foam used for the "Polyurethane Foam Caulking" have a higher set temperature and/or density to preclude the use of other off-the-shelf types of polyurethane foams.  I think this would be good for quality control.