An interesting experience.... last winter I applied Storm King Heat Shrink Window Film on the windows. This is the stuff that you tape the plastic around the window frame and use a heat gun to shrink it to a pretty clear, invisible film over the window.
I figured I'd have to take it down during the summer, but surprise !! The shrink wrap actually is keeping the house cooler !! Guess the layer of air is keeping heat out of the house.
There are a lot of windows which I don't use, so I'm keeping the window plastic on year round. the shrink wrap stuff stays almost crystal clear.
Even with screens, flies manage to get into the windows but the plastic stops them.
I had a window with a venetian blind fitted into the casement... just adjusted the blinds the way I wanted and sealed the window off with shrink wrap, over the top of the venetian blind. It's been working really well... can't adjust the blinds, but they were adjusted well to begin with
fwiw
Peter