It might be useful to remember that all "fiber" wads are not "created equal" when it comes to obturation. Cork wads, for example, do not obturate much, at all. Fiber wads can obturate a bit better, especially if they are properly lubed and/or "ventilated" (see Zutz). By and large the best obturators are felt wads, with obtuation levels varying according to the quality of the felt and the wad lubricant that is used (See Greener, Churchill, et.al.).