Storm windows and doors are a second set of windows and doors. They provide insulation by creating air space between themselves and existing windows and doors. This air space reduces heat loss through the glass. Windows can lose heat through conduction or infiltration.
Clear Plastic Storm Door
Storm windows can be made of either glass or clear plastic and can be installed either inside or out. Clear plastic can be taped to the inside of the window frame. This doesn't last long, but it does reduce infiltration and conduction at a low cost and it's easy to install. Mylar is available instead of plastic - it does not tear and is easier to see through.
Rigid Plastic Installation
A third method is rigid plastic purchased in a kit that consists of a self-adhesive frame and a clear plastic sheet that can be sized to the window. A more permanent method is to install storm windows made of glass with metal our vinyl frames.