Last weekend, I started my testing of what was not waterproof on the bike. Firstly, I put a bowl with a brick in it in each liner bag and let it sink into a bucket of water. Within a minute there was a centimetre or so of water in the bowl in every case. I first suspected that the seal over the seams was going, but then I saw water seeping through the material itself. Actually, more than seeping since there was a slight pressure differential between the inside of the bag and the outside.
Given that I had already suspected they were not fit for purpose, I’d done some shopping the first Tuesday back and spent about $150 on new 20 litre waterproof sacks of the same brand as the one I transported my Eeepc in. They don’t have seams, and hopefully will last another 15 years. At the same time I also bought a new Thermarest; the technology improvements mean that the new one is about a quarter or less of the packed size of the old one. It’ll fit right in a pannier and not need to be strapped to the outside (but should fit neatly strapped to the front panniers).
My next test was to see if the rear panniers were letting water in. I took one out the back and applied the hose test for a few minutes at full bore. Nothing inside got at all wet, so I decided to try something more interesting and placed it in the shower for about 15 minutes. Again, nothing inside got wet. That leaves me puzzled as to why water was able to seep through the liners if it couldn’t get through the pannier. I guess I have to wait until a wet day and just go riding for several hours (or leave them in the rain all day).