There are a lot of different types of materials that you can end up using if you want to make use of business cards and the like, but once all has been said and is now out of the way perhaps the best material that you can utilize in this manner would be metal. The reason behind this is that metal is an incredibly durable material and on top of all of that it can help your business cards to stand out a lot more than might have been the case otherwise.
That said, you should remember that there are various metal types that you would have to choose from when making Black Metal Kards as well. Ideally, you should opt for a metal type that has a bit of bendiness to it. Creating cards that are a bit too stiff will make them a bit dangerous to handle, and you can see this for yourself if you were to have cards of this variety printed in the first place. The harder a metal is, the more brittle it would end up being as well which further shows that bendy metals are the way to go.
Using metals that are relatively flexible will make it so that you would end up getting the chance to maximize the durability of your business cards to a rather high degree. Finding your ideal metal is all about trying to figure out what matters most to you. If your highest priority when it comes to business cards is durability, it makes a lot of sense that you would want to opt for a metal that is relatively flexible and will not break at the slightest pressure.