R-value only measures a given insulation's ability to stop heat transfer through conduction. A product such as fiber glass or cellulose may achieve a high R-value but will still allow air to pass through it, thus allowing heat transfer, through way of convection.
R-values alone are almost worthless. R-values are measured in airtight, zero weather condition capsules. This is not an accurate way to measure something that will be on the outside walls of a house, that will constantly be indirectly exposed to several weather conditions and varying wind speeds. Consumers should know how the insulation will react to water, wind, mold, sound, etc.
Furthermore, most kinds of insulation lose R-value when the temperature drops. This is because the material itself gets colder with the temperature. If the material is colder, it will be less effective in stopping heat transfer by conduction. Different types of insulation will differ on how much R-value they will lose. For instance, studies have shown that fiber glass insulation loses 40% of its R-value when the temperature drops below 20. In a standard 2x4 stud cavity fiber glass achieves an R-14 at best and can drop down to an R-8. Foam insulation does not suffer from this effect; in fact it increases in effectiveness when temperature drops. This is because the cells that make up foam insulation hold gasses and hinder the foam from getting colder. It is because of this that Styrofoam coolers work so well.
To many, the solution for air flow is to use fiber glass batting that has a vapor barrier on one or both sides. When you use fiber glass with a vapor barrier you need ventilation so that vapor can escape before building up moisture and causing all kinds of damage. However, if vents are in place, air flow is present which allows heat transfer through convection. There is just no way to win with fiber glass. Cellulose has all of the same weaknesses as fiber glass. Cellulose will settle over time, it does not stop air flow, and will require added insulation in later years.
RetroFoam uses Tri-polymer based resin injection foam for enclosed cavities such as existing walls and Icynene spray foam for open cavities. Foam insulation will not settle or crack over time. It is moisture resistant and most foam insulation is non-flammable.
Foam insulation is excellent for sound deadening. Different products may vary on these qualities, be sure to research every product and company. Foam insulation R-value is usually higher then cellulose and fiber glass. However, with all these other benefits, R-value is the least important of its qualities. Foam insulation is the way of the future, it is the product huge corporate buildings want to use because of how effective it is, and any homeowner can have the same product.