Carlson Pro Pets Wall Mount Defender Pet Door-Medium The most heavily insulated pet door available; Insulation material has an R Value of 45, encased in an indestructible aluminum flap Training tool provided to acclimate your pet to its new door Features security lock and quick attach stainless steel security panel Incredibly easy installation, expandable tunnel in wall mount version fits walls from 4.75 Inch to 8.25 Inch with no cutting of the frame required Medium Opening Dimension 16"l x 10"w