The pieces that Loki has with waterproof ratings fall within these three levels:
8,000mm - Rainproof and Waterproof under light pressure (Light rain, average snow, light pressure.)
10,000mm - Rainproof and Waterproof under light pressure (Light rain, average snow, light pressure.)
15,000mm - Rainproof and Waterproof except under high pressure (Moderate rain, average snow, light pressure.)
Manufacturers typically describe the waterproof breathability of fabrics using two numbers. The first is in millimeters (mm) and is a measure of how waterproof a fabric is. In the case of a 10k or 10,000 mm fabric, if you put a square tube with inner dimensions of 1” x 1” over a piece of said fabric, you could fill it with water to a height of 10,000 mm (32.8 feet) before water would begin to leak through. The higher the number, the more waterproof the fabric.
The second number is a measure of how breathable the fabric is, and is normally expressed in terms of how many grams (g) of water vapor can pass through a square meter (m2) of the fabric from the inside to the outside in a 24 hour period. In the case of a 20k (20,000 g) fabric, this would be 20,000 grams. The larger the number, the more breathable the fabric.