Allen writes from Milpitas, California: "Some of your FAQ and responses reference an insulation compression chart, where R value vs amount of compression is indicated. No amount of creative searching using your search capability of your web site would reveal this chart.

I am interested in finding out the loss in R value if I compress your R21 fiberglass wall insulation into a 5 inch cavity instead of 5.5 inches. You might want to confirm this is a common issue since it is impossible to find actual dimensioned 2" lumber. Pretty much anyone who wants to furr-out a 2x4 wall to accept 2x6 sized insulation will probably end up with 5 inches instead of 5.5 inches.

I've heard the R19 insulation, which starts out at 6.25 inches becomes R18 when compressed to 5.5 inches. I really don't know how to figure R21 compressed by 1/2 inch. Knowing the R value of R19 compressed to 5 inches would be nice too."

Answer: The compression chart is still in the website. I am sorry you had a problem finding it. For your convenience, I have included a link to the chart to in this answer.