Staying dry on the inside is near important as keeping the moisture out.
The top level of outerwear uses a waterproof/breathable material. It works by not only stopping moisture from coming in, but also allowing from the inside moisture out.
A DWR is used on the outer layer as first line against moisture coming in. Second layer is a membrane which creates another barrier for water coming in, but also a valve for moisture to escape.
The lining layer wicks moisture from your body towards the membrane. If a garment is rated at 10,000/10,000, it means that the garment can cylinder over 24 hours before it leaks. The second number is breathability. 10,000(grams) of vapor can pass through a square meter over a 24 hour period.