Curtains blackout linings

Blackout loose linings are designed to allow customers to create a blackout effect will still using readymade curtains rather than have custom curtains made.These linings have a 1″ heading tape and fix behind your existing curtains, with no need for sewing. They simply hang on the same hooks or gliders as your main curtains. These linings are beautiful quality, 3 pass total blackout fabric (Supersoft Deluxe Blackout), well maufacturer with straight, neat seams and cut straight meaning they will hang straight. What size?
It is always best practice to match the size of the loose linings to the size of the main curtains(if the face curtains are 66″ width then use 66″ width linings).