Hey, I have driven my friends Toyota Prius 2014 which he had installed these Ground Zero sheets from Sound Works. He added these sheets into the doors only. So, I realised that there is no such a huge difference. Yes, It does have a difference but not the major impact. So, I think if we need a better sound insulation then we must cover the whole interior with these sheets (including; Roof, Floor, Pillars, Doors etc etc). Then, we may find a huge difference. One more thing, that I liked so much in his car that not doors become more heavier than ever. It was a great touch and sounds so great whenever you open/close the doors.