Measure the outside portion of your air conditioning unit.
Choose an insulated air-conditioning cover sized appropriately for your air-conditioning unit. Search for a thick variety that contains insulation, rather than a thin, simple cloth cover. Look for this at your local hardware store.
Cut a piece of rigid foam insulation to the size of the area between the side of the air conditioning unit and the edge of the window. Use a utility knife.
Window air-conditioning units typically have an accordion-style adjuster that often fails to keep hot
in or cold air out.
Fit the foam insulation in the area between the window frame and the side of the air conditioning unit.
Tape the foam in place using aluminum insulation tape. You can find this tape at your local hardware store.
Press a foam insulation strip between the window frame and air-conditioning unit, starting in the corner.
Cut the end of the strip off and discard the excess.
Push the strip in place, using the rounded end of a butter knife.