Insulation Behind Tub Area Walls

So I have the tile all demo'ed, studs exposed. The fiberglass insulation is not in bad shape, but its texture is a bit "mushy" when you squeeze it. Easy enough to rip out and replace with new. Possible it may have been exposed to moisture. So, should I replace with new fiberglass insulation or use some other material, perhaps foam board? Ideally, something that would prevent future mold or mildew growth because of exposure to high humidity. I will use cement board and thin set mortar in front of it, but I think it may still be exposed to moisture.