Waterproof coatings

 
Each manufacturer has their own way to make a tent waterproof, UV resistant and at the same time breathable. The waterproofness of the material is rated in mm and this is a spec you want to look for: Numbers go between 800 mm and 10,000 mm.

The number refers to a water column height in millimeters. For example, 1500 mm means that the fabric will withstand a 1500mm (5') column of water for more than one minute before a single drop might appear through the fabric. That's strong enough to prevent rain from leaking in a 75 mph hurricane-force storm. In the outdoor industry, they use this number as shorthand to describe the amount of coating used to make the nylon or polyester tents waterproof. Some people may also refer to this value as the hydrostatic head pressure.

The general consensus is that from 800-1000mm on, the material is waterproof. BUT, it is better to have a high water column because coatings will wear off, and the waterproofness value will decrease.

The PU (polyurethane) coating is one of the strongest and most abrasion-resistant kinds of coating, but manufacturers usually don't tell what coating they use so you'll need to contact them to find out. PU optimizes the waterproofness and strength while still being light-weight. Manufacturers can maximize the amount of coating only to a certain point. More coating means more weight and more cost. Also chemicals in coating weaken the fibers, so at some point, increasing the water column value too much will decrease the fabric strength. This is why 10000 is the highest value you can find.

From my personal experience a 7000 mm Ripstop fly, which was used in rough condition, with poor maintenance (I didn't know better) started to leak after about 500 nights of use. There are no test standards or easy ways to verify the water column value for products on the market so you have to trust the manufacturer.
 

Related Articles

 
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How to make your tent last many years longer?
Free standing tent (geodesic) VS. Non-free standing tent (tunnel)
Why do I need a good tent? Which are the best brands on the market?
Bivies/Hammock/Tarps: An lighter alternative to tents
 

 


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