The lining decides what the blind does
The face fabric is what you see and the lining is what the blind actually does. An unlined Roman filters light and shows the fabric's texture; a blockout lining darkens the room and gives the blind more body. It is worth deciding what you want the blind to do before you choose what you want it to look like, because the lining is not easy to change later. In a light, unlined fabric — what most people mean by a sheer Roman — the battens that set each fold show through as fine horizontal lines when the sun is behind it.