Experiments that target the B-mode polarization signals in the Cosmic Microwave Background require more sensitivity, more detectors, and thus larger aperture millimeter wavelength telescopes. These larger apertures require ever larger vacuum windows to house cryogenic optics. Conventional vacuum windows, such as those made of High Density Polyethylene (HDPE), require a corresponding increase in the thickness of the window material to handle the extra force from the atmospheric pressure. Thicker windows cause more transmission loss, increasing survey times, thermal loading and decreasing sensitivity of the instrument. We have developed the use of woven High Modulus Polyethylene (HMPE), a material 100 times stronger than HDPE, to manufacture stronger, much thinner windows. We will discuss the fabrication and characterization of new thin laminate vacuum window recipes, including mechanical and optical tests, with the goal of developing a new window for BICEP Array cryostats.