What is the R-value of rigid insulation?

One advantage you will find is that rigid insulation R value is higher than in traditional insulations. In rigid insulation you'll find R-values as high as R-88.7, compared to a high of R-3.5 for traditional insulation. 

Types of Rigid Insulation

• Molded Expanded Polystyrene (MEPS) – bonded polystyrene beads. High density MEPS provides up to R-4.0.

• Extruded Expanded Polystydrene (XEPS) – extruded polystyrene crystals and additives melted and pressed into boards. R-Values: up to R-5.0 per inch.

• Polyisocyanurate – closed cell with low conductivity gas. R-Values: R-5.6 per inch.

• Polyuethane – uses low conductivity gas and foil or plastic facings. R-Values: 8.7 per inch.