Read somewhere else that using plastic wrap on windows would lower temp 30 deg. Can I use wrap that comes in rolls at WM or do I have to buy the plastic wrap kits? Thanks!
As was said, adding clear plastic would reduce conduction of heat into the house by increasing the total R value of the window.
But, most of the heat gain through windows comes from the sun shining through the window. Clear plastic won't do much to stop that.
The best technique for reducing solar gain through the window is to put something on the outside to block the sun. This might be landscaping, a trellis, and overhang (if its a south facing window), or one of the solar screens that block a lot of sun radiation, but still allow a view.
Some ideas here: http://www.builditsolar.com/Projects...ve_cooling.htm
(in the Shading section)
Window "tint" is most likely what the original poster is referring to - it will decrease temp. gain in a room exposed to the sun.
Lots of those "platic wrap" kits will not allow the window to be opened (or air to flow through the window) - so if you're in an area with cool night breezes you could potentially take advantage of - your insulating plastic wrap may actually end up costing you money (or comfort).
Bubble wrap is supposed to be very good insilation. I put it on unused windows and my skylights during the winter months. Works good they say and I guess it does by my experience but you sure can't see out of them. It gives a stained glass effect. Still, its good for where you don't need a view and dirt cheap. Rolls of large bubble wrap are only $3 or so at Wallyworld. All you do is spray on some highly diluted dish washing detergent and it sticks there till you remove it for the season. I just roll mine upwith masking tape and mark it for what window it came off. More of a winter thing really but it could work for you.
We are in North Texas and the West sun blazes against our windows! What we did this year, because the Solar Screens helped but with that kind of sun you need a LOT more, we got the bubble wrap that is reflective on each side and bought the tape so we could cut and tape it to fit our windows. It is insulation and found by the insulation at Home Depot.
Then we measured each window so that we could slip the reflective insulation between the solar screens and the windows and so they would be reasonably easy to remove come October, when the heat isn't an issue. So make it an inch smaller than each side of the window. You will get a little solar gain this way but not much, otherwise you will never get the stuff between the screen and the glass.
It is like foil in that it reflects but putting it between a solar screen and the window you can even see the shine.
It took about and hour and half cutting, taping and installing it. We had 6 good size windows and one small one in the upper bathroom. And, although you can't see out those west windows, it has made a HUGE difference in the heat upstairs.
On the lower floor I am making awnings lined with this stuff, so it looks good on the outside but under the fabric it is the reflective stuff.
I think we have about $80 invested in it and I had enough to make an bodacious solar oven!
I wouldn't use anything clear because it is the radiating heat that gets magnified through clear glass or plastic, think of your car in the summer and how it heats up through the glass. That is the same way clear plastic would work. ANYthing Reflective needs to go on the OUTside of the windows if you have double or triple pane windows because the reflection will pop the seal on those windows.
Here's a photo of my solar oven before I added to flexible wings to it, you can see what kind of material Im talking about.