Crypto Key Stack can be purchased at cryptokeystack.com. The black anodized stainless steel plates offer fire protection up to 2,200°F — well above the temperature of a house fire. Also claims to be waterproof and rustproof. Comes with its own engraver.
You can either engrave or stamp your seeds onto these stainless steel cards. Engraving was pretty easy, though the granularity of the engraver leaves a bit to be desired — it would be easy to screw up a letter in a way that makes it ambiguous to read, such as a B versus an 8 or 1 versus l.
Heat Stress Test
The screw near the heat deformed slightly and was very hard to unscrew, but I managed to loosen it with pliers. I really don’t like how small the heads on the screws are; I think products like this should use pretty heavy duty hardware.
Corrosion Stress Test
The acid removed some of the black anodization from the outer plates, but the inner plates were completely unaffected.
Crush Stress Test
Performed admirably under pressure; after prying the layers back apart I was still able to read all of the data off them.