Reflective Bubble Insulation Sheet, Double Side Aluminum Foil Bubble Shield, Aluminum Foil Thermal Insulation Radiant Barrier for Windows, RV, Roof, Garage Door (47IN X 10FT)

I bought some of this: https://www.amazon.com/dp/B0CH9K4L44, cut it out in the shape of the windows, and then finished the edges with a little fabric. One roll was more than enough for all windows.