Lining your curtains is usually a good idea, and offers the following benefits:
- curtains hang better,
- gives you more privacy,
- blocks out more light,
- keeps in more heat,
- gives better insulation against noise,
- makes curtains last longer - the lining protects them from fading and dirt,
- gives a uniform appearance to windows from outside (if the linings match).
In addition to standard lining fabrics, there are flame-retardant linings, and fabrics that totally block out light.
A thermal interlining (an additional layer of fabric between the curtain and lining) improves both heat and sound insulation, and makes the fabric look much fuller.