you got a point there Fred....I've had blue balls before but never purple......lol.....Fred61 said:It should be pearlite. I don't think styrofoam balls would survive the mixing process. There must have been some serious stresses on the board in order to have the balls turn purple. IMHO.Flamegrower said:Hey fellas I was at Home Depot to buy some non combustible backerboard, they had both Hardiebacker and Durock.....I had bought Durock before but as I was loading this Durock on the cart recently, I noticed it had little styrofoam balls encapsulated in it.....that CANNOT be good for fire rated walls.....I imagine they did that to cut down on the weight a little, but I would not trust using that as a non combustible backer.....I held a map gas torch against some 1/2" Hardiebacker for several minutes (till it was glowing orange on one side) and you could still touch the other side with your bare hand.....I would trust the Hardiebacker board over all else esp. in a situation like mine where you are going to install tile or stone veneer.......just my two cents.....