I want to soundproof a bathroom, and am planing on replacing the existing sheetrock walls in the bathroom using DensArmor drywall. Will this product significantly reduce the noise caused when someone is showering, running water in the sink or flushing the toilet? Also, is it feasible to insulate between the studs with fiberglass blankets or styrofoam? I don’t want to do that if it’s just going to be a place for mold to grow.
Here are a few things to consider when soundproofing a bathroom. First off, Georgia Pacific's DensArmor Plus 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, DensArmor Plus 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 you can do is to evaluate the pipes where they are. You can soundproof a bathroom by using foam insulation like Great Stuff to isolate and insulate the pipes from the surrounding structure, and can also add rubber spacers between the water supply pipes and the studs. Once this is done, it's okay to add fiberglass insulation before installing the DensArmor drywall.
Another inexpensive trick-of-the-trade you might want to consider is to double-up the DensArmor using a product called Green Glue in between the layers. Green Glue is an acoustical soundproofing material designed just for this purpose, and will help soundproof your bathroom.