It's nice of you to chip in and share some additional information, particularly about Jameson Lopp's new tests. They seem to have performed nicely although there were problems with the heat stress tests with both the Coinplate Alpha and the Coinplate Grid. He had difficulties unscrewing the fasteners and taking the plates apart, but in the end he managed to do it.
You can read our comments on the tests in our blog post. The units that Jameson Lopp tested were shipped to him around half a year ago. Since then we improved the manufacturing a bit, so the screws are not as tightly fitted as before. It should mitigate some of those problems.However, the important thing is that Coinplate will survive a house fire, even if it's abnormally hot. House fires burn at around 600°C/1100°F (at max can get up to 850°C/1500°F), and it survived a much higher temp of 1093°C / 2000°F in that test quite fine.
The most important thing for a backup is to survive and protect your seed phrase. If after a terrible disaster your only worry is to open your quite intact backup I think that's great. Even if it may require using some extra force, a hammer or maybe a power tool in some worst cases.
Coinplate is made using 2 thick stainless plates joined with solid screws that are set using threads in the plates, without a separate washer. Each Coinplate weighs 1.2kg / 2.5 pounds, so you are getting quite a heavy-duty unit. It is a stainless steel sandwich made from two plates each 5mm (3/16") thick.
A little quibble, to be meticulous. On your website, the weight is 1.14 kg.Is the total weight of the plates really just over 1 kg? I can't imagine that plates with the indicated dimensions weigh so impressively (of course, relative to another).
My finger must have slipped, I meant 1.1kg. Yeah, that's how much our backups weigh. The weight of each is between 1.13-1.14 kg.
You don't have to just trust me, you can make the calculation yourself using for example this steel weight calculator. The dimensions for the whole unit are 10 x 105 x 138 mm. The material is 304 stainless steel which is stainless 300 series in this calculator. The calculator computes the weight as 1.15 kg or 2.53 lb, but there is some slight material loss during the processing (i.e. rounded corners, mounting holes, polishing). Screws fill their sockets almost entirely, though.
Silicone or rubber doesn't have the same high resistance to various media as stainless steel, which means that if exposed to adverse conditions, it will be destroyed faster than plates. This will lead to the fact that an "aggressive" substance can penetrate into the gap between the plates, which will put this storage medium at risk. This is my verdict after theoretical considerations. 
Thank you for your very detailed answer and detailed explanations. This allowed to look at your product from a different perspective.
Thank you for your very detailed answer and detailed explanations. This allowed to look at your product from a different perspective.
That's the same conclusion we have arrived at, after making some mockup designs. Glad that I helped and thanks for the interesting discussion.
They seem to be using different numbers on different parts of their website. The main page says it weighs 1.3kg:
Sorry for that dumb error on our site and inconsistency. As explained above, each Coinplate weighs between 1.13-1.14 kg. Thanks for pointing it out though, I'll review our site for errors.