Understanding Waterproof Rating and Breathability
Manufacturers typically describe the waterproof breathability of fabrics using two numbers. The first is in millimetres (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.
All outerwear designed for active winter sports has various degrees of water resistance, but will eventually leak given enough water, time and pressure. Manufacturers define “waterproof” according to different standards, and testing is not standardized. A rubber raincoat is completely waterproof and may be the ideal garment for standing in a downpour waiting for the bus, but if you tried to ski or snowboard in it, you’d be wet in no time from your own perspiration. The trick is to balance protection from rain and snow on the outside with the ability to let water vapor (warm perspiration) escape from the inside.
One thing to remember for most puffer jackets and vests, the fabric may have 5000mm waterproofing, however as the garment has been stitched with the baffle to create the puffer look, this reduces the level of waterproofness because water will be able to drip through the stitching.
|Waterproof Rating (mm)||Water resistance provided|
|0-5000mm||No resistance to some resistance to moisture|
|6000-10000mm||Rainproof and waterproof under light pressure|
|11,000-15,000mm||Rainproof and waterproof except under high pressure|
|16,000-20,000mm||Rainproof and waterproof under high pressure|
|20,000mm+||Rainproof and waterproof under very high pressure|
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