if i made a sleeve for an external hard drive, what could i make it out of that would block magnetic waves? (even if i dropped an industrial strength magnet on to it by mistake)
An alloy called mu-metal. But this is not something about which you need be concerned; you will not find sources of stray magnetic fields around your computer which will be strong enough to cause problems.
Distance is the only protection. the magnetic force follows the inverse square law. The strength of the force is weaker the further from the source you get. Nothing stops it, and the only thing that might effect it is a magnetic material (iron, nickel) which would itself become a magnet in the presence of these forces. You can only keep things away from magnets, you can't sheild them. Dont confuse them with electromagnetic force, which can be redirected trough sheilding. very different things.
