I've heard its very tough, Mark from SBC told me the rep demoed it to him by sealing the empty saddle bag up full of air and jumping up and down on it.
I have to says the weight is surprisingly reasonable considering that they tend to be overbuild (e.g. their panniers), I did liked their little valve that enable you to compress the bag properly.
I'd still go for a Revelate Design Viscacha that £20-30 more.
anyone used any of the ortlieb bikepacking stuff?