Moisture vapour transmission (breathability) is an important attribute for waterproof clothing.
The moisture vapour transmission is denoted by the “Moisture Vapour Transmission Rate” (MVTR), and is given in g/m²/24h. This value indicates how much moisture vapour will pass through a square metre of fabric in a 24-hour period (g/m2/24).
This means:
the greater the MTVR value, the better the moisture vapour transmission rate and therefore the breathability.