Hi suzi. Certain coatings or materials on the inside of the dishwasher, such as stainless steel, are more durable, retain heat better, and can withstand higher temperatures than materials such as plastic. These higher quality materials may increase the appliance’s efficiency, but there may be also be extra initial cost. Some models marketed as Hybrid will use both materials in the tub, often using stainless steel on the interior door to increase durability on the part of the appliance with the most common wear and tear.