Just read a few post about membrane jackets and thought it worth making a few comments which might or might not be useful.

Waterproof membranes in clothing come in different grades, often seen refered to in mm (millimetres). You might hear or see 5000mm on a description or ticket on the garment.
What this means: Water resistance can be measured using a standard test of a square tube (approx 25mm across) on top of a small square of the membrane. This is then filled with water to varing heights marked on the tube, when the water starts to seap through then this measurement records how resistant the membrane is. So 5000mm = 5 meters high of water was put into the tube before the seaping started.

More info on Waterproof Ratings and Breathability Guide | evo

Membranes are Gas permeable. Which means that only vapour will pass through, not water, so if the water has condensed on the inner shell it will get wet inside. High activity generating sweat and heat, vapourises the water and therefore will flow through the membrane. Once you slow down, cool down then the water might start to condense, as like a boiling kettle, the steam can be seen rising, but once off the boil the steam condenses and forms water droplets. This can happen on the inner side of the garment, as there is not enough heat to keep the "steam" going and the outer side of the jacket is cold. Windows demonstrate this really well. Moisture inside the car or building condenses on the cold glass. Double Glazing helps prevent this, but not always, as the inner glass is warmer than the outer glass.

Our Top tip is to know the membrane you have in your garment and to use it accordingly.

Rugged & Tough.