Abstract: An apparatus and method for sizing warp yarn utilized in preparing a loom beam for weaving are disclosed. A porous application roll (A) is utilized for applying a sizing material onto a sheet of warp yarns (12) passing between a pressure roll (30) and the application roll. The application roll includes a continuous cylindrical porous application surface (B) formed around the entire periphery of the roll having an extent at least as great as the warp yarn sheet width. An intermediate porous distribution layer (C) is provided next to the application surface (B) for disbursing the sizing material onto the application surface. A porous flow control membrane (D) having a pore size less than that of the distribution layer occupies a boundary region for metering the sizing material. When the passage of warp yarns is discontinued, the application roll (A) is moved to an idle position by an actuator (38). In the idle position, liquid (72) is made to contact the application surface to maintain it in a moist condition.