The cat hair which could not be removed after vacuuming the curtains with a brush attachment can be removed with the help of following process. Prepare a mixture of one part of liquid fabric softener. Spray this mixture with a spray bottle on the area of the curtains where cat hair is attached. A light spray is needed and the fabric softener will loosen the hair which will make the removal much easier. Let the mixture dry and then vacuum the curtains. Allow the liquid on the curtains as it will give a fresh fragrance to the room. The process can be repeated as often as required. Wash the curtains in due course as the fabric softener will start building up.