Lining is the part of a curtain nobody sees and everybody notices the effect of. It determines how the fabric falls, how much light and heat it holds back, and how long the curtain lasts.
Why line at all?
Four reasons, in roughly this order of importance.
It improves how curtains hang. An unlined curtain is light and tends to flutter and crease. Lining adds weight and body, so the fabric falls into proper folds and holds its shape.
It protects the face fabric. Sunlight fades textiles, and it does so quickly on a south-facing window. Lining takes that damage instead.
It insulates. A significant amount of household heat is lost through glazing. A lined curtain creates an air gap that slows that loss.
It controls light. How much depends entirely on which lining you choose.
Standard lining
Usually a cotton or poly-cotton sateen in ivory, cream or white. This is the default and it suits most rooms.
It adds body, protects the face fabric and provides modest insulation. It reduces light without blocking it — a room will still be usable in daylight with the curtains closed.
Choose it for: living rooms, dining rooms, hallways, and any window where total darkness is not required.
Blackout lining
A dense three-pass coated lining that blocks essentially all light through the fabric itself.
One thing to be clear about: blackout lining blocks light through the curtain, but light will still enter around the edges. For genuine darkness you need generous overlap at the centre, returns at the sides that meet the wall, and a pole positioned well above the window. The lining alone will not do it.
Blackout is also heavier and stiffer than standard lining, which affects how the curtain drapes and increases the load on your pole.
Choose it for: bedrooms, nurseries, and rooms used for watching screens.
Thermal lining
An insulating lining, usually with an acrylic foam or metallised backing, designed specifically to reduce heat loss.
It is the most effective option for insulation, and worth considering for older houses with single glazing or large expanses of glass. Many thermal linings also provide substantial light reduction, though not always full blackout.
Choose it for: draughty rooms, single-glazed windows, north-facing rooms, and anywhere heating costs are a concern.
Interlining
Interlining is a separate soft layer — usually bump or domette — sandwiched between the face fabric and the lining. It is not a substitute for lining; it sits in addition to it.
The effect is transformative. Interlined curtains are noticeably thicker, fall in deep sculptural folds, insulate far better than lining alone, and absorb sound. They are what gives high-end curtains their characteristic weight and drape.
The costs are real: interlining substantially increases weight, cost and bulk. An interlined pair can easily be three times the weight of the same curtains lined only, which has direct implications for your pole diameter and bracket spacing. They also take up more space when stacked open.
Choose it for: formal rooms, period properties, large windows, and anywhere you want curtains to feel genuinely luxurious.
Matching lining to hardware
This is the step most often forgotten. Heavier lining means a heavier curtain, and a heavier curtain needs a stronger pole.
Unlined curtains are fine on a 19mm pole. Standard lined curtains suit 28mm. Blackout or thermal lined curtains on a wide window want 28mm at minimum with a centre bracket. Interlined curtains want 35mm or larger, or a heavy-duty track.
If you are upgrading existing curtains to a heavier lining, check that your current pole is still adequate before you order.
A note on light versus privacy
These are different problems. A lining that blocks light from outside also prevents people seeing in at night when the room is lit. But a lightweight unlined curtain that looks opaque in daylight can become surprisingly transparent after dark. If privacy matters, test with the lights on and stand outside.