What jokir44 said!! In spades!!!
I am a pre-wetter. I wet down most everything that comes into my house because I have an alergy problem with the sizing in most fabric. I rinse stuff in as hot a water as I can stand and then dry in a dryer. It gets rid of enough of the sizing so that I can work with it comfortably and also controls shrinkage. But precut flannel is something that I would never even think about pre-wetting.