fizik saddle bag - waterproof?

I've currently got a topeak medium aero pack and to be honest it's far too big for what I need, however what I really don't like about it is that it's not at all waterproof and on a rainy day everything inside it gets soaked. I was thinking of changing it for one of the small fizik packs that can clip onto my fizik saddle and whilst the size looks perfect I'm not sure if it's going to be any more waterproof than what I've currently got. Any experiences with it?
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TREK 2.5 training and commuting
GIANT REVEL 1 LTD for when it gets all snowy
but for mudguardless deluge riding, definitely not, probably no bag would be
It's not all out monsoons that my current one's suffer from though, the spray from the rear wheel on only slightly wet roads is enough to soak everything in my topeak one which obviously isn't good for mobile phones or £10 notes!