True, but it seems like the max weight for a letter/postcard is 3.5 ounces (~99 grams), also a postcard is about 148x105mm while a microSD is 15x11mm.

I would propose making your postcard out of a 9x9 grid of 1TB microSDs and tape to give you an 81TB postcard that can be delivered overnight at the minimum price while providing 11.25 Gbps given the numbers you used.

Sobering to think of the true (hardware only) price of that postcard in full view of anyone handling it: $36k ($450 * 81).

But amazing to think how far technology has advanced.

Exchanging data and money offline, in a very compact format :-)

These metrics fail to account for the transfer to a more stable medium, or even just a single full read of the data.