First off, Home Depot occasionally offers a deal – buy so many cases of fiber and get a 24 hour rental free. It’s not every day, so I can’t tell you when, but I’m hoping if you’re planning on going this route, that either it’s free or at least available on the day you want it! Secondly, the variable R-Value is because YOU, the blower, can choose to fill a space or not fill it. The lower the amount you stuff in the wall, or lay down in your attic, the lower the R Value. The more you fiber in the wall or on the floor of your attic, the higher the R Value.