Worked very well when putting Polk DXi 6.5s in my 98 Ford Ranger. Not very thick plastic, but that worked for me, since I didn't have much room behind the factory door panel. They are way more convenient than making your own adapter. You'll have to drill your own holes for the speaker mounts, and/or dremel them out a tad if your speakers need a larger cutout, but I used the measurements beforehand and they worked perfectly. Very nice.