I'm thinking most liners they sell are blackout liners, which reduce the amount of light coming into the room. These are being sold to be used along with your unlined drape. They could be installed on rings and pulled separately behind a panel. Roclon is a fabric choice for lining, which provides a neutral color to the street side and protects your face fabric from the sun. I prefer to use a heavier lining such as thermalsuede, or blackout lining and usually add interlining, a flannel lining, for extra body and insulation when fabricating window treatments.