What's the cheapest way to protect an external HDD from things like solar flares and EMP pulses? I periodically save all my data on an external HDD, so I may as well make it a proper digital doomsday vault. I have shittons of tinfoil, if that's any good. The HDD won't need to be opened more than maybe once a year, so it doesn't have to be as sleek as the expensive commercial bags.