should be close to R11/R13. The R19 I used before was too thick(3.5 inchs), and my final(?) configuration involved reducing it's thickness by 1/2, to approx. 1.75 inches. 2.54cm to the inch, I think 5cm/50mm thickness would be "ideal". SamI looked at the R13 I used for my sun room, even that looks a bit thicker/denser than what I ended up with after "splitting" the R19.