FlashCo's TPO FlashAccessory Inside and Outside Corners are Factory Certi ed prefabricated ashings made from 60 mil reinforced TPO membrane. They are designed to provide a 6" ange in all directions from potential leak points at corners. FlashCo o ers both inside and outside corner designs for interior facing 90° parapets and concave corners as well as exterior facing 90° curbs and convex corners.