In reply to Tom Ripley Mountain Guide:
> Have you got a link to back that up?
> I don't see what is wrong with a down bag and a goretex bivi bag.
You will be soaking from the storm hitting before you got the ledge up. Water will be everywhere, in everything, on the ledge floor, running down your clothes whenever you reach out. You will probably be in your bag with some wet clothes on and with you wet harness on, clipped in with wet lengths of rope. If you got it wrong you might even be in a small water fall (El Cap is topped by slabs so the run off down the face can be considerable) as many routes follow the kind of features that water likes.
There will be much unpleasantness. However, the temp (in summer) is not that low, so with modern synthetic stuff you should be fine. Just damp.