Which insulation method minimizes heat flow through windows?

• A. Sealed windows (vacuum)
• B. Fiberglass
• C. Bubble wrap
• D. Aluminum foil

Answer: (A)

Minimizing heat flow through windows hinges on cutting off the paths heat uses to move: conduction through the glass, convection in the air gaps, and radiant transfer. A sealed window with a vacuum eliminates the air between panes, so there’s virtually no medium to carry heat by conduction and no air to circulate heat by convection. That leaves very little heat transfer overall, making it the most effective option among those listed.

Other methods don’t address all those transfer modes as effectively. Fiberglass is a good insulator for walls, but a window still has solid glass and gaps that conduct and convect heat, so its benefit is limited in this context. Bubble wrap traps air, but without a true seal and the proper gap spacing, it can’t prevent convection or provide the same level of reduction in conduction. Aluminum foil mainly reflects radiant heat, which helps with solar gain, but it doesn’t eliminate conduction and convection through the window assembly and can be less practical for a building’s glazing.