I plan on replacing the sheetrock walls in the bathroom using the Dens Armor drywall. Will this product significantly reduce the noise caused when someone is showering or running water in the sink or flushing the toilet? Also, is it feasible to insulate between the studs with fiberglass blankets or Styrofoam. I do not want to that if it is just going to be a place for mold to grow.
Dens Armor is made by Georgia Pacific and is a terrific product for mold-proofing your bathroom. Instead of having a traditional paper face which can feed mold, Dens Armor has a fiberglass face which can not feed mold. However, as good as it is, it is not designed to reduce sound transmission by itself.
Reducing sound starts with a good building design that, for example, doesn’t route the main plumbing waste pipe through the dining room ceiling! Assuming that you don’t have the ability to re-run pipes, the next best thing might be for you to do is to evaluate the pipes where they are. Use foam insulation like Great Stuff to isolate and insulate the pipes from the surrounding structure. Add rubber spacers between the water supply pipes and the studs. Once this is done, it is ok to add fiberglass insulation before installing the Dens Armor drywall.
Another inexpensive trick-of-the-trade you might want to consider is to double-up the Dens Armor using a product called Green Glue in between the layers. Green Glue is an acoustical sound-proofing material designed just for this purpose.