Dirt, gravel or other debris may prevent the door from sliding and sealing optimally. Replace existing curtains with insulating thermal curtains. Thermal-lined curtains are thick, insulated curtains that block drafts and help prevent the loss of heat through windows and doors.

Insulate Sliding Glass Doors with Shower Curtains Hanging a heavy duty clear plastic shower curtain liner with clear plastic dollar store hooks on a tension rod would definitely help.