I've done a bit of "kitchen sink" testing. It seems as though after a while water penetrates through the fabric itself in the seat area. The seams look fine. I don't know what gives these liners their waterproofing - this test suggests it may be a coating which has "worn" through being sat on, but there's no sign of any delamination or "flaking" that I've seen on PU products in the past. When I get time I'll take them into my dealer and see what they say.