There are an optional range of lining options including blackout linings and interlinings for improved insulation.
Normal ivory lining is the standard for the majority of curtains
Blackout lining is a popular choice for children's bedrooms, night shift workers and so on. Despite the name they are not black but a densely woven white coloured heavy lining. They completely prevent any passage of light through the curtains. There will still be some light leakage round the edge of the curtain.
Interlinings are well worth considering when you buy new curtains for your home. They act as an extra insulation layer within the curtains and can help reduce energy bills.
There are two options. Bulk interlining is available on pencil and eyelet headed curtains and provides excellent thermal retention. There is also a lightweight thermal bonded lining which can be used with pencil, pinch or eyelet headed curtains. Ask your consultant for more details.