R value insulation ratings are used to measure insulation's ability to resist heat flow. The higher the R value, the more effective it is. House Insulation should be purchased based on its R value, not thickness or weight. One type of insulation maybe thicker or thinner, but if the R value is the same they should insulate equally.

R value performance testing is done in a 70 F environment with no air movement. Ironically enough, when you need insulation the most you're generally not in these ideal temperatures or conditions. This can result in the rated house insulation R value being higher than the actual effective R value.

The R value in house insulation is substantially lowered when there's any air or water/moisture leaks. This is why traditional fiberglass insulation is often ineffective. In addition, it becomes a breeding ground for dangerous molds.

1 inch of insulation is = to 30 inches of concrete.
There are different types of house insulation materials, each having a different R value.
A comparison of various insulation materials are:

House Insulation R value of Blown in Cellulose Insulation is 3.70 per inch
House Insulation R value of Fiberglass Insulation is 3.14 per inch
House Insulation R value of Expanded Polyurethane foam is 6.9 per inch
Thermal Performance Myth. There is a widespread belief that all insulation materials of equal R-value will perform equally.

Thermal Performance Fact. While insulations of equal R-value perform equally in the controlled conditions of a laboratory, they do not all maintain that R-value in the walls and ceilings of a building. Some give off gasses to the atmosphere and suffer a decline in efficiency, while the performance of others is vulnerable to the installers' shortcomings.
'Thermal Drift' as this phenomenon is politely called, results from the failure of materials to fill all cavities completely, thus leaving air pockets which permit air movement inside the cavity. Further 'drift' occurs with some materials if the insulation is not fully protected against air infiltration, both from the interior and the exterior. Commonly used insulation may well perform at a fraction of its' nominal rating depending on installation, how well it fits the cavity and how well it is protected from air infiltration.

Helps stop air and moisture infiltration thereby by eliminating an environment for mold spores and bacterium to take hold
helps save on energy costs
can add strength to a building structure
helps keep dust and pollen out
barrier to vermin and bugs