Windows are one of the weakest parts of your home's insulation envelope. Heat can leak out of your home during the winter and into your home during the summer. If you are worried that you are paying too much to heat and cool your home, a good place to start is by upgrading your windows. You may want to entirely replace your windows, but in some cases, you can save yourself money simply by upgrading the windows you already have.
The conventional way to improve the insulation provided by your windows is to use more than one pane of glass. The additional sheets of glass will do little on their own to isolate the interior of your home from the outside world, but they do allow you to sandwich a layer of gas between the layers of glass. This trapped gas will separate the inside pane from the outside pane.
Thus, when the inside layer heats up with the air from your furnace, the wind on the outside of your house will not be able to rob your house of heat. While the multiple panes of glass will not be able to completely protect your home from the outside air, they will help.
A window film will protect your home not by insulating the inside of your home for the outside world in the typical way. The sun's UV rays can pass right through your window no matter what sort of gas you put between the panes of glass. Once inside, these rays will then heat up the interior of your home during the summer. During the winter, the heat from your furnace will leak out through your windows. By installing window film on each one of your windows, you can filter out the sun's UV rays during the summer and reflect heat back into your home during the winter. In fact, window film can reduce your cooling costs by up to 23% and your heating costs by up to 25%.
The only way to keep your energy costs down is to do everything you can to improve your home's energy efficiency. If you are looking for a quick, inexpensive remedy that will give you a lot of bang for your buck, then you want window films. If you have the money to spend, finding multi-pane windows with window film will give you even better separation.