Methods and apparatus for providing a chemical mechanical polishing pad. The pad includes a polishing layer having a top surface and a bottom surface. The pad includes an aperture having a first opening in the top surface and a second opening in the bottom surface. The top surface is a polishing surface. The pad includes a window that includes a first portion made of soft plastic and a crystalline or glass like second portion. The window is transparent to white light. The window is situated in the aperture so that the first portion plugs the aperture and the second portion is on a bottom side of the first portion, wherein the first portion acts a slurry-tight barrier.