One of the special attributes of Yixing teapots is the ability to retain heat. Small pores produced in the clay during firing retain both heat and flavor, and the low shrinkage rate of Yixing clay allows the skillful potter to make a closely-fitting lid that inhibits oxidation thus heightening the teas flavor. The Yixing teapot is free of lead, arsenic, cadmium, and other toxic materials. Yixing ware is unlike other unglazed earthenware teapots. The Yixing teapot has a fine and solid texture, a four percent water absorption rate, a very low thermal conductivity, and a double air hole design which enhances the pots brewing properties. The principal standards for evaluating a teapots brewing quality are the color of the tea soup produced and the level of tea phenol, caffeine, and aminophylline. The performance of the Yixing teapot is far superior to that of the standard teapot with respect to all four of these criteria. Not only are the Yixing teapots beautiful and unique works of art, but also, they are excellent brewing vessels