1969-70 Plexi Glass Fastback Rear Window. Plexi Glass fastback rear windows will save nearly 30 lbs of weight. Constructed of 0.25" think Plexi Glass. It’s no secret. Track cars flex during cornering and acceleration. Because of this, glass windshields are prone to crack. Eliminate this problem with one of our new light weight Plexi Glass windshields! Our Plexi Glass windshields weigh a lot less than the stock glass windshield and are formed as the originals to fit into the stock rubber gasket. $15.00 box fee applies. Shipped truck freight only.