"A [1974] test on conventional window shades showed... 1) A roller shade inside a with 1/4" gaps at the sides of the shade reduced heat loss through a single glazed window by about 28%. 2) A drape drawn in front of the... window reduced heat loss by about 6%. 3) A venetian blind reduced heat loss by 7%.During the summer the shading devices reduced heat gain by the following... 1) white, opaque roller shade 50% 2) venetian blinds (slats at 45%) 18% 3) venetian blinds (slats closed) 29%"