Cheap window coverings ususally aren’t lined with the exception of sheers. Sheers are just that, sheer, a fabric to allow light into the room through the fabric.
Lining a window covering is a standard in the custom world of window fashions, it is a given. What does the lining add to the window covering? Lining adds body to the overall treatment. Lining protects the expensive face fabric from sun rot and fading, therefore extending the life of the treatment. Another function lining performs is it aids the overall window fashion in visual performance, in other words it hangs better and therefore looks better. When you consider the low cost of the lining itself it is well worth the money.
