A slat for use in a window frame having opposing walls may include a wing portion structured to block light, the wing portion having a first end in a longitudinal direction and a second end opposite to the first end; and a first pressure contact part provided at the first end and a second pressure contact portion provided at the second end, the first pressure contact part and the second pressure contact part being structured to press the wing portion against the opposing walls of the window frame to thereby hold the wing portion in place.