Hoklartherm Universal Retractable Roll-up Roof Shade CurtainsHoklartherm Universal Retractable Roll up Roof Shade Curtains Hoklartherm's retractable curtains, made in Germany, use aluminum fibers to create a drier, fungus free environment. Available in various sizes for most greenhouses, each curtain is 8 feet long and made from white FFS 4 4 aluminum and acrylic fabric. Providing 55 60% shading, these curtains are expertly designed and manufactured.