Does it work? Yes
Average noise reduction: 5 dB
Cost per door: RM 5
Get it on Shopee: https://invol.co/cl2iuzf
Get it on Lazada: https://invol.co/cl2iuzy
English blog post: https://helmihasan.com/dshapedoors...
Malay blog post: https://helmihasan.com/my/dsealpintu/