Can I add insulation to double pane gl?

I want to add a layer of foil faced styrofoam to the inside of a double pane picture window. The window has argon gas between the panes. The foil would be against the gl. The heat in the room caused by direct sunlight radiates into the room right through the window shade and will raise the room temperature by 3-4 deg F in 20 minutes. I have heard that this could break/shatter the gl.