“5D” car floor mats are an advanced type of custom-fit mats that offer highly contoured coverage of the vehicle’s flooring. The “D” often refers to depth and detail in fitting—typically these mats cover the footwells, edges, door sills, and sometimes even parts that “3D” mats don’t reach well. They typically have multiple layers (for example rubber / TPE top, foam or EVA middle, anti-slip or backing layer) to address durability, comfort, and protection.