Because they work.

I tend to agree with the other Ortlieb folks that posted above. I have toured extensively in some very wet conditions, and have never had any problems. Coated codura nylon does not breathe, If it did, it would leave moisture in about as easy as it lets moisture out of the bag. That is a myth started by Arkel; as is the myth about mold/ mildew in waterproof panniers. If you are in a situation where condensation is going to be a problem it isn't going to make any difference if it is a waterproof or a water resistant pannier.

I have inadvertently left my rack pack open on a picnic table during a downpour; and all it took was dumping out the water, and drying it with my towel. I also store my wet tent in an Ortlieb rackpack without any adverse consequences (inside a sil-nylon stuff sack and a plastic grocery bag). There is no cross contamination with the dry goods, my sleeping bag and Thermarest.

My wife and I experienced 35 days of rain on one tour, and much of our camping gear stayed damp for long periods. Not a problem.

If I ever have to replace my Ortlieb panniers, it will be with Ortliebs. Having said that, I still use a pair of Nashbar front panniers on my everyday bike. It is ridden almost daily in Oregon's wet winters, and the panniers are still waterproof after 10 years of use. They were also the front panniers I used to ride across the U.S.

Try this with loaded non-waterproof panniers. Washing the mud off after riding through the flood area near Calgary, Alberta, 2013



This was one of the 35 days of rain, much of which was ridden on unsurfaced roads and trails.



I've used this picture at at least 3 dozen times, but it does illustrate the conditions when waterproof panniers shine It was after this tour that we opted to replace our non-waterproof bar bags with Ortliebs. That orange cover on my saddle is the rain cover from my non-waterproof, wet bar bag.