MDF rings under the speakers are used to install new speakers in cars where speakers with atypical mounting are installed from the factory. They are made on a CNC mill and fit exactly into the door. Compared to plastic mats, MDF mats have the advantage of being adjustable. In addition, they are ecological and do not burden the environment as soon as they reach their end of life. They are sold in pairs and are impregnated. If you are concerned that there is high humidity in the doors of your car, we recommend purchasing plastic pads.