The effect of masking and veiling of the private space(s) is the main interest, as well as the effect that public versus private has on the boundaries in human conduct from a psychological point of view.
The window is a portal to the outside space. The curtain is the boundary between the interior and the exterior. Being sheer the curtain allows the character to see the outside world, but at the same time acts as a barrier isolating the character in. Eventually the character and the barrier merge into one. The character becomes universally engulfed in its own psychological barrier.