I hate to say it, but even the Volkswagen Passat has the same sort of cardboard on the top of its roof. It's bigger though but still very disappointing when you see it.

I did extensive soundproofing to my car (Passat) before so I know.

I didn't exactly hold the 2 boards, but they sure look like card boards to me with the VW logos on them. I'm not surprised if that's really the case either.

What's important actually is the headliner itself, the headliner used in my car and other continentals are made of thick foam and cotton textile, so the sandwich board they use between the headliner and the metal roof can be just corrugated cardboard pieces or some sort of treated resin.

The other luxury cars like BMW (latest models) and Mercedes (W204, W212) also have like boards in their roofs just like VW. Lexus actually uses 3M thinsulate in their door panels, can also see thick sponge like foams stuffed in the B pillars as well.

Actually that's not true. Comparatively speaking - stock to stock on a rainy day - comparing a typical Japanese sedan vs the Passat. Most mainstream Japanese car roof are just bare metal with a thin piece of headliner, so the roof really does sound like those zinc roof houses... very noisy. The Passat had corrugated cardbox pieces in between and a thick headliner piece so noise was also naturally a lot less so...

And when you factor in the prices - if we assume RM100 is the cost of soundproofing per car vs RM10 for cardboard pieces, the savings is rather substantial when you look at the number of cards they produce every year.

Same. Even the German luxury 3 continentals also doing the same things for their rides.

It's a mainstream car, there's no reason to spend more than they should. The profit on mainstream cars are low enough as it is.

The headliner is actually the immediate ceiling where you can touch, it's actually a combination of the plastic frame, the cotton or leather cover and a thick or thin piece of foam inside that covers the metal ceiling, so the corrugated cardboard piece acts as insulation.

So what I have now is a vibration dampening mat that is pasted on bare metal roof sheet, the stock corrugated cardboard piece is placed between the dampening mat and another piece of heat and noise insulating foam layer and finally covered by the headliner. Needless to say, the noise from heavy raindrops is more drastically muted and surprisingly there is a noticeable improvement to the bass of the audio and the overall audio quality. Using a sound meter registered about 2 to 3 dBA drop in ambient noise.