The Dallas Energy Code has prescriptive insulation requirements for walls and ceilings. The following a list of value ranges depending on which manufacturer the insulation comes from.

We will use the average value for our calculations unless the product is clearly labeled differently or you have some documentation that indicates otherwise.

Material	R Value Range	Average R Value
Fiberglass blanket or batt	R  2.9 – 3.8	R  3.2
High Performance fiberglass batt	R  3.7 – 4.3	R  3.8
Loose fill fiberglass	R  2.3 – 2.7	R  2.5
Loose fill rock wool	R  2.7 – 3.0	R  2.8
Loose fill cellulose	R  3.4 – 3.7	R  3.5
Perlite or vermiculite	R  2.4 – 3.7	R  2.7
Expanded polystyrene board	R  3.6 – 4.0	R  3.8
Extruded polystyrene board	R  4.5 – 5.0	R  4.8
Polyisocyanurate board unfaced	R  5.6 – 6.3	R  5.8
Polyisocyanurate board foil faced	R  7	R  7
Spray Polyurethane foam	R  5.6 – 6.3	R  5.9
Reflective foil with foam core	R  14.5	R  14.5