R-values for SIPs depend on the thickness of the SIP and the type of core material that is used. See SIPA’s R-value chart for the minimum R-values of commonly available SIPs.
Static R-values, like those included in the chart, rate the effectiveness of insulating material. However, they do not accurately describe how products perform in a real world setting. When fiberglass or other types of insulation are installed, they are installed around structural members made of wood or metal that have very poor insulating value. Field-installed insulation materials are also prone to installation imperfections.
The Department of Energy’s Oak Ridge National Laboratory has studied and tested the performance of entire wall assemblies in large sections. The resulting whole-wall R-value data reveals that a 4-inch SIP wall rated at R-14 outperformed a 2×6 wall with R-19 fiberglass insulation.