We put a total of 4 Blackout Indow Inserts in to 3 windows in our Master bedroom. The center window was too wide to use a single insert. I was given an excellent explanation by the Indow sales consultant, Martin, about how the mullion bar would work, prior to deciding to proceed with requesting the laser measuring kit. Our Master bedroom is on the back of our home, which has a very busy major street running behind it, and also happens to be on the west/sun-setting side. I have always encountered frustrations installing curtain rods and even then, blackout curtains seem to still let in more light than my wife and I wanted. The Blackout Indow Inserts have addressed the light issue so much better than any blackout curtains ever could. The sound reduction from the traffic and a significant temperature reduction in our bedroom are bonus aspects to these investments in our home. The Inserts were easy to press in to place and fit perfectly. My wife and I are extremely pleased with the results and highly recommend Indow Window Inserts