Patio doors are cold in the winter

The patio door in the kitchen gets extremely cold in the winter. Turning up the heat has no noticeable effect. Curtains are not enough. The thin plastic film that people shrink into place using heat from a hairdryer gives little insulation value. I purchased two 2x8’ sheets of 5/8” plastic foam insulation and duct-taped them into place against the patio glass panes, on the outside surface. Using them on the inside surface of the glass would have created a toxic smoke and fire hazard, according to the label on the board. During cold snaps, the change in the temperature of the kitchen has been dramatic. It is now quite comfortable near the patio door. The furnace runs less frequently. The plastic foam boards don’t look pretty, but they’ll come off in the spring.