Polycarbonate Clerestories Daylighting Curtain Walls: Custom built curtain or window walls are a wise. The Sundance Supply approach is a Multiwall Lexan Polycarbonate sheet and the Base & Cap Installation System. The customer provides the frame and remaining building components, for a custom wall system. Together this approach provides a watertight, attractive and long life solution. – Also See 40mm Thermoclick 4.47 r-value.