I inquired at an art supply store about finding flexible, rolled material that was opaque. I was told that 'opaque' is not really absolute here and that under strong sunlight it would slightly 'glow' if used on my window to block out sunlight.
Seems it is difficult to find a TRULY opaque material unless one buys dedicated 'darkroom cloth'. Are there suggestions to counter this dilemma? I have one: heavy duty aluminum foil as a cost effective solution. Are there others? Please understand that standard poster board will ALSO glow on the inner side if direct sunlight hits it. - David Lyga