It varies with the thickness of the insulation
Generally, about R-3 per inch. 3 1/2" for a 2x4 stud cavity is R-11. 5 1/2" for a 2x6 stud cavity is R-19. But if there is any airflow it greatly reduces the insulating value. Also, the thermal bridging of wood structures reduces the performance of fiberglass insulation.
fiberglass
As strange as it may sound dead or still air is one of the best insulators. Insulation such as fiberglass or rock wool and styrofoam work because they are fluffy with trapped air. If you have a sheet of four inch thick R40 fiberglass and squeeze it into a wall made of 2X3 studs you will have less R value than than a 3 inch piece of fiberglass insulation. So the highest R value goes to the insulation that traps the most dead air per inch of thickness and is installed propperly.
Many products are 30+ these days.
Fiberglass Insulation, R Value of 3.14. Pine board has an R Value of 1.74
Every insulation has a different R value. It ultimately is determined by which insulation you will be using. Now lets do rough estimate. 4" thick, regular fiberglass mat has R-value of 13. Assuming that plywood has the same to half the insulating value of fiberglass, 1/2" plywood would have 1/8 to 1/16 of R-value of that 4" mat. Roughly R-1.6 to R-0.8
I am not sure where you heard this but the thickness of old putty against the thickness of insulation for r-value is not as good. The best insulator is air. Fiberglass insulation has a high r-value because of the air it holds not the fiberglass itself. So that's why you don't cram 6in fiberglass into a 4in space, it does not work when you compress it.
Poured concrete has an R value of about 0.08/inch. Fiberglass batt has an R value of about 3.14/inch (blown fiberglass wall insulation is about 3.2/inch). From these values we can calculate that the equivalent insulating thickness of concrete would be about 3.5x3.14/0.08 = 137.4 inches. Note that concrete blocks have a somewhat better insulating value due to the incorporated air pockets. A 4" concrete block has an R value of about 0.2/inch An 8" concrete block has an R value of about 0.15/inch A 12" concrete block has an R value of about 0.1/inch
it is a good thing i think R Value is the thermal resistance of a given material. The higher the R Value the more thermal resistance and the better the insulation. So, an R48 roof system is warmer than an R32 roof system. All insulation materials are rated by their R Value. An inch of rigid insulation has a higher R Value than an inch of fiberglass insulation. Check with the insulation manufacturer for the R Value.
Yes they r
technically unfaced fiberglass insulation has an r value of 21 for 6 inches but that's if its perfectly installed, no gaps, no crushes, no air moving through it, no moisture, and its completely in contact with the interior heated surface. Since its unfaced, we assume it will have moisture and air moving through it and an average installation, it's likely R-13 or less.
r-30
10 inches corresponds to about R-38.