A thermal insulating apparatus for insulating a building envelope is provided. The thermal insulating apparatus may comprise at least one panel comprising one or more layers of insulating material, and at least one attachment site for joining the thermal insulating apparatus to at least one position of said building envelope. The thermal insulating apparatus may be operable between an open position allowing access to a wall opening, and a closed position in which at least one panel of the thermal insulating apparatus substantially covers and thermally insulates said wall opening. The thermal insulating apparatus may further comprise at least one solar thermal energy collector unit for collecting heat from solar thermal energy from sunlight, and the collected heat may be used for heating a structure such as a home or garage.