Yesterday one of the resident teenagers in my house informed me that the wall in their bathroom was collapsing. Upon inspection you could see tile coming loose, and the wallboard in back of them soggy and crumbling. Argggh ! The damaged area is big enough that I am considering installing one of those four piece tub surrounds. But I will have to remove all of the tile and repair the wall first. If I were putting tile back, I know what backer board to use, it's 1/4 in thick and sold in the tile section of Lowe's. However, since this will be in back of the tub surround, I was wondering if one of the drywall type products would work. Looking at them in the drywall isle, I saw codes, like "MR", "TE", and "X" . Is the "MR" moisture resistant ? It was kind of a green color face ? Of course there was no clerk to help. Could someone offer suggestions as to the correct product to use for this application ?