Bubble paper makes great insulation because air is a good insulator, and bubble paper is nothing more than bubbles of air wrapped in plastic; bubble paper is cheaper and easier to use than other, traditional alternatives; and it can be reused many times.
Insulation is any substance that protects one space or material from the temperature variations of an adjacent space or material. Any substance can act as an insulator, though some are much better insulators than others. The ability of a substance to act as an effective insulator depends on how it resists temperature changes and how quickly it can dissipate heat.
Air and Bubble Paper
Air, particularly air in a confined space, is a good insulator because the air inside the space tends to resist temperature changes. The air inside changes temperature slowly because the air molecules move around, making transfers of energy (heat) between one molecule and another more difficult to accomplish. Bubble paper is nothing more than plastic wrapped around many individual volumes of air; thus, the air inside helps bubble wrap to resist temperature changes. Bubble paper shares this feature with cavity wall insulation "by combining with the still captive air, the insulation acts as a barrier to heat loss" according to The Environment Site.
Bubble paper can be attached to windows simply by spraying water on the window first and then spreading the smooth side of the bubble paper over the wet surface. To apply a double layer of bubble paper, tape can be used to attach the second layer to the first.
One of the greatest things about using bubble paper as an insulation material is that it can be used again and again, so long as it remains in relatively good shape. If you can keep children (or yourself) from popping all the bubbles, then the bubble paper should be usable for many, many seasons. However, if your intention is to use the bubble in summer and winter, you should use a UV resistant bubble paper to ensure longevity.
Bubble paper is not clear, so when it is used to insulate windows that window can no longer be see out of. Also, the plastic of the bubble paper can deteriorate with exposure to UV. It would only last a year or two if it were kept on a window year-round. Additionally, bubble paper is not a great insulator in extremes temperatures.