Storm windows are so effective because they basically trap a layer of air between themselves and the window. This dead air space acts as an insulator, thus reducing heat loss. They will pay for themselves in fuel savings in the very first year.
Insulation from cold or energy efficiency are the main concerns with a window. One option to reduce electricity consumption is to choose a window with good insulation properties, however storm windows are more efficient and less expensive. Even better, you don’t have to remove the old windows to install the storm windows, so you can further save on expenses. Basically, storm windows are a great solution to increase energy performance inexpensively, they provide sound insulation (reduce noise from the outside), reduce window condensation and let in fewer UV rays, thus protecting furnishings.
Storm windows can be installed either on the exterior or the interior of the primary windows. When ventilation is necessary, they can be easily removed. Interior storm windows (a.k.a. inside storm windows) are usually better, because they are not exposed to the climate so they get scratched and damaged less. In addition, they are fitted more tightly and are less expensive.
When it comes to materials used to make windows, glass is the most commonly used. It offers visibility, looks good and is the most durable. On the other hand, it is more prone to damage and can be easily broken. When you are installing inside storm windows, however, the risk of damage is relatively low. For outside windows another material might be better. Other types of windows include plastic panels and special plastic sheets, but they don’t look as good as glass storm windows.