"It keeps the heat in but also allows light and heat to come through too. You put the bubble part on the window and it traps the condensation which dries up by the sun during the day."

How effective is bubble wrap on windows?

How Effective Is Bubble Wrap as Insulation? The bubbles in bubble wrap serve as multiple insulating pockets filled with air. Some sources claim that on a single-pane window, bubble wrap can reduce heat loss by up to 50%. On a double window, heat loss is estimated to be cut at around 20%.

How can you stop condensation on windows overnight?