Steel woks coated with non-stick coatings such as PFA and Teflon, a development originated in Western countries, are now popular in Asia as well. These woks cannot be used with metal utensils, and foods cooked in non-stick woks tend to retain juices instead of browning in the pan. As they necessarily lack the carbonizing or seasoning of the classic steel or iron wok, non-stick woks do not impart the distinctive taste or sensation of "wok hei". The newest nonstick coatings will withstand temperatures of up to , sufficient for stir-frying. Woks are also now being introduced with clad or five-layer construction, which sandwich a thick layer of aluminum or copper between two sheets of stainless steel. Clad woks can cost five to ten times the price of a traditional carbon steel or cast-iron wok, yet cook no better; for this reason they are not used in most professional restaurant kitchens. Clad woks are also slower to heat than traditional woks and not nearly as efficient for stir-frying.