What insulating materials have the highest R-value?

R-value is resistance to air flow. The higher the R-value, the more efficient the insulation material is.
One of the major factors that determines R-value, is what the insulating material is composed of.

Insulating materials and R-values:
There are many different types of materials that are commonly used in the insulation of a building. Some of these materials are more efficient than others. The following is a list of common insulating materials, arranged in order from least to most efficient.

- Rock wool : R-Value per sq. inch = 2.5
- Loose fill fiberglass : R-Value per sq. inch = 2.5
- Standard Fiberglass batts : R-Value per sq. inch = 3.1
- Icynene Spray : R-Value per sq inch. = 3.6
- Blown cellulose : R-Value per sq. inch = 3.8
-Polystyrene Board : R-Value per sq. inch = 5.0
-Polyurethane Rigid Panel : R-Value per sq. inch = 7.0
(Wikipedia, R-Value)