Since the 20th century, nylon is one of the most common materials for the construction of carpets. Both nylon 6 and nylon 6-6 are used. Nylon can be dyed topically or dyed in a molten state (solution dying). Nylon can be printed easily and has excellent wear characteristics. Due to nylon's excellent wear-resistance, it is widely used in industrial and commercial carpeting. In carpets, nylon tends to stain easily because of the dye sites which exist on the fibre. These dye sites need to be filled in order to give nylon carpet any type of stain resistance. As nylon is petroleum-based it varies in price with the price of oil.