The Patio Pacific Thermo Sash 3e Cat Door is the premium solution for adding a Cat Door to your sash style window. It is far more energy efficient than cheaper single pane Cat Doors for sash windows, and combines dual-pane, low "e" glass with the superior, award winning Endura Flap (see below). It is highly wind-resistant and includes a "draft stopper". The Thermo Sash 3e Cat Door is constructed of beefy metal framing and has a sturdy locking flap cover. The spring loaded design ensures that this Cat Door can be installed and removed in seconds, no tools are required for installation. There is even a couple of built-in "anti-whoops" features that allow you to adjust your panel by 3/4" to make a perfect fit or even make corrections to your installation, just in case your measurements are slightly off.