The BOROUX Foundation™ Black filter elements each have a different filter speed, how is this possible?

You can! This is because no BOROUX Foundation™ Black filter element is the same, they are all unique. As a result, one filter element may run through faster, than another. The differences occur during production (baking process) and you often see that the filters in the same box are more or less the same, but this does not have to be the case. So it is otherwise not a problem and not something to worry about.