I accompanied my ex-colleague a few years ago to a Puchong car accessories shop where he installed SIKA brand Sika Damp 610. 

Does it work? Yes for sure. His Myvi was slightly quieter while driving and it rained on the day he installed it and inside the car, the heavy raindrops were a bit muffled compared to standard.

Please take note that this soundproofing job is a whole day's work. The installer has to remove the seats, carpeting, roof panel, door panels, etc... then when applying the Sika Damp material, the installer had to use a heat gun and also a roller.

Unfortunately, that particular Puchong car accessories shop has closed down during the Covid-19 pandemic.