Energy efficiency can be increased by sealing the bottom of your door with a threshold. These adjustable thresholds perform as well as their conventional cousins, however they also have the ability to raise or lower the vinyl seal as required to seal against the bottom of the door. They compensate very well for door sag and also for doors on which the bottoms may have been mis-cut during installation. M-D Building Products offers different style door bottoms to fit your specific application.