I was walking down the street the other day and realized that a worker was covering the windows of a bank with a clear film. It was crystal clear and invisible once it was applied. After some research I found out that it was probably the 3M Window Film.
This is what I found out about it: 3M Window Film is a super durable film, as seen in the picture, that you stick on the exterior of your windows. It protects the glass, covers cracks and holes, filters UV rays and other factors that cause fading of the color of furniture, hardwood and fabrics and a specific type also reflects heat and fights over-heating in summer. Under many circumstances, this can be a step to save some electricity and money spent on maintenance. Remember that sun can fade and yellow paperwork, magazines, books and photography so much faster, and I'm telling this from experience.