The Round Back Vent exhausts out hot air from the attic in the summer and moist attic air from the attic in the winter, while preventing rain and or snow from entering the roof. Having a round design makes the Round Back Roof Vent aerodynamic, thus allowing it to deflect wind and objects carried by the wind. Insects and vermin will also not be able to penetrate the roof vent. The Round Back Vent with curb mount flange is engineered to be mounted on top of a roof curb. The curb mounted flange allows for easy access to the opening of a roof curb if maintenance of the attic, fan or duct below is needed. All of our roof vents are durable, lightweight and will never rust. They always look like new, even years later. Color: Aluminum.