Although not gluing the insulation down sounds like a good idea, without a molded insulation and carpet it would never work. If your car has any sort of tranny hump, the only way to keep the insulation and carpet in the shape of the hump is to stretch it and glue it down. Although mmetalman does have a point about the insulation in luxury cars, personally, its not worth my time to go to a junk yard and look for a Cadillac, then remove the seats, the center console, and all the side plastic trim to remove the carpet to get to the insulation. And the insulation will be molded to fit the floor of the car you get it from, and wont be anywhere close to the floor in your car. Not trying to be a dick and shoot down anyones opinions or ideas down, just trying to put everything into perspective.