Custom drapes are an investment so protecting them and making sure they look great long term is important. Enemy number one is the sun. To help with this, adding blackout lining and interlining will provide the most protection against the sun and elongate the lifespan of your drapery by creating a barrier between the harsh rays of the sun and the fabric.
Man-made fabrics or synthetic fabrics are generally more color resistant due to either the color being ‘built-in’ to the fiber, or the ability to take stronger more caustic dyes. As with anything, the darker and more saturated the hue, the more prone to fading it is. But even with the right lining, all drapery fabric is susceptible to fading/damage over time.
If you have a very wide window and the fabric you’ve fallen in love with will break the bank, consider decorative side panels instead of full drapes. Meaning, the drapes you select won’t completely meet in the middle and cover the entire window. They are meant to be stationary. But if you need protection from the sun consider adding blinds or shades that can be raised and lowered as need to block the sun. With or without blinds, you’ll still want to add a protective lining to your drapery.