In order to insulate single glazed windows, I have been experimenting with secondary glazing film. I don't know what material it is, but I am guessing this could be polyprop made very thin so it is transparent - is that right? However, it gives the windows a slight haze which is annoying. I have tried cling film (aka cling wrap) but it has the same problem and is also less durable. I did some research online and discovered polycarbonate film, but it seems too expensive. I guess there is always clear polystyrene (the stuff that cd cases are made from) but it would probably have to be a few mms thick because it is not very strong. However it is pretty low cost material so it might be suitable. I know people often use acrylic sheet and polycarbonate sheet as secondary glazing, but these options cost $50-150 per window, and I am aiming for $10-20 or less. Any suggestions would be most appreciated?