Voile is a soft, sheer fabric, usually made of 100% cotton or cotton blends including linen or polyester. The term comes from French, and means veil. Because of its light weight, the fabric is mostly used in soft furnishing. Full-length curtains in hot countries are made with voile and used as window treatments, mosquito nets etc. When used as curtain material they are similar to net curtains.
Here are some good examples of voile curtains I found on the web.