Can someone please tell me what these are? I've read that when changing front bumper that you need to buy these. Is this true?

Do you need to buy them? Or do you not need them?

Forgive the possible stupid question. lol

 

Brake ducts channel sufficient air from the front of the car through the front brakes to remove the large amounts of heat generated by severe and prolonged brake use. Just as proper brake components (calipers, rotors, pads) are required to convert the kinetic energy of the spinning rotor into heat, so must the necessary air be moved in, through, and out of the brake system to remove the heat (energy).

17 is the Brake Air Duct
RealOEM.com * BMW E60 545i Trim panel, bumper, front