As you can read about on the insulation page, the most effective, affordable insulator is still air. Even your batts and blow in type insulations rely on this. They are really just a matrix with hundreds and thousands of gaps, each filled with motionless air.
You can see that bubble wrap is similar. Different brands have different amounts of bubbles and different sized bubbles. These bubbles play the role of the insulator.
Also, plastic by itself is an insulator. Bubble wrap is really two layers of plastic pressed together in a way that allows bubbles to be formed. These layers act as an insulator too and have a different coefficient for conducting heat than glass.
On a more expensive scale, you can get acrylic sheets, insulating films and double or even triple glazing. These all work on the same two basic principles that bubble wrap as an insulator that give bubble wrap its properties. Of course, bubble wrap is much cheaper, if not free!
As there are no nails and there is no glue to hold the bubble wrap onto the windows, it is great for renters. Also it’s light, portable and easy to clean
Bubble wrap can be wrapped firmly but not too tightly around almost anything. We even bubble wrap sone of our potted plants in winter
Wipe down the window so that it is clean
Measure and cut the bubble wrap to fit the window glass
Make the window glass damp, even a little wet
Press the bubble wrap against the glass starting on one side and pressing it down as you move across to the other.