Sheer curtains can provide a certain level of privacy, but they do not offer the same level of privacy as opaque or heavier fabrics. Sheer curtains are typically made of lightweight, translucent materials that allow light to pass through while partially obscuring the view from outside.
When the sheer curtains are closed, they can create a soft, diffused effect, allowing you to maintain privacy during the day while still allowing natural light to enter the room. However, at night or in situations with bright interior lighting, the sheerness of the curtains may make it easier for people outside to see into the room, especially if the room's lighting is brighter than the exterior lighting.
If privacy is a significant concern, you may want to consider using additional window treatments in conjunction with sheer curtains, such as blinds, shades, or heavier drapes. These options offer more opacity and can be closed for increased privacy when desired.
Ultimately, the level of privacy provided by sheer curtains depends on factors such as the thickness and weave of the fabric, the lighting conditions both inside and outside the room, and the proximity of neighboring buildings or spaces.