Hello, We recommend Jewel's Tape which is available in 3/8" from The Workroom Marketplace. workroommarketplace.com/collections/sewing-supplies/products/3-8-jewels-tapes
Hello, Elki's course RIBBED ROMAN SHADES demonstrates how to construct a blackout Roman Shade from start to finish. You can register for this self-paced, online course through The Workroom Channel at the link below: workroomchannel.pathwright.com/library/ribbed-roman-shades-cortinas-romanas-acanaladas-18951/about/