Is the size the only difference between the medium and large PlexiDor? The medium and large size PlexiDors are constructed the same way. The medium door is suitable for dogs up to 40 pounds and the large for dogs up to 100 pounds. In a multi-pet household, a smaller dog or a cat is usually able to open these doors without problems. Both models have a saloon-style design, a cylinder lock with key, and they are delivered with a metal security plate that screws to the frame on the inside of the door. The doors are available for installation through a house door, through a wall, or as a glass kit. The aluminum frame is available in white, bronze, or brushed aluminum.