The company are Huiaacoustics of Guangzhou, PRC - just across the border and where we used to live, actually.
They replied to two queries amazingly promptly and in English. I've been dealing with Ms.Jane Qiu and think using the contact form on their web page would get you a response. I used Google Translate to append a Chinese version of my query as a courtesy, which I'm sure is appreciated. If one can private message on this forum I'd be happy to pass in her email address.
contact us form
The company make soundproof doors, panels and portable barriers. On their website I can't actually trace the product they suggested by email but I'll upload an image and the specifications that they emailed. It should appear someone in this post.
Size: Standard sizes are 1mx2m, 1mx2.1m and 1.2x2.3m. The size is customisable up to a massive 3mx5m, Jane said.
Weight: The blanket is 40mm thick and the weight is about 2.7 kg/m2. So for our (huge) apartment door roughly 10kg in weight but easily liftable.
Price: They have standard sizes, priced at 545 RMB /m2 or HKD $664/m2. For their 1.2x2.3m product that's about HKD $ 1,832. I'm not sure if there are any taxes on top of that, as yet.
Delivery: Delivery to Sai Kung is estimated at HKD 300 (they'd provide a better quote if we go ahead with the order, I asked for a guess only).
Sound blocking: Sound reduction is measured in decibels and despite a degree in physics I had to reacquaint myself with such, ha! A 10dB sound reduction = sound perceived as being 50% as loud. A 15dB reduction is perceived as roughly 40% as loud and a 20dB reduction about 25% as loud. (Anyone jump in and correct me, please.)
The blanket offers "sound blocking 15-25dB" so as a minimum should reduce the noise to 40% as loud. Bear in mind the blocking depends on the frequency of the sound. I don't know how effective it would be at blocking a door slam. It also depends on a close fitting with no gaps, ideally.
For our needs - to cover a door - we would have to construct a wooden frame to hold it over the door at night, and of course hold without gaps around he edges. I'm still working this out - trip to Apliu Street to buy more tools maybe :-)
If go ahead and get one of these I'll post an update. Oh, on the thickness of the doors - yes it's a huge factor. An acoustic door sealing kit (round the edges) would be good, I believe, but 50% of the sound or more may be coming through the door. One could "do the math" but this suggests that an acoustic sealing kit may need an ally in the form of a bl**dy great sound-absorbing blanket!