There are tradeoffs between waterproofing (hydrostatic head measured in mm) and breathability (measured in g/m^2/24h), but "one or the other" isn't really accur

There are tradeoffs between waterproofing (hydrostatic head measured in mm) and breathability (measured in g/m^2/24h), but "one or the other" isn't really accurate, there are products that do very well at both.