<P> A tea bag is a small, porous, sealed bag containing dried plant material, which is immersed in boiling water to make a tea or an infusion . Classically these are tea leaves (Camellia sinensis), but the term is also used for herbal teas (tisanes) made of herbs or spices . Tea bags are commonly made of filter paper or food - grade plastic, or occasionally of silk . The bag contains the tea leaves while the tea is steeped, making it easier to dispose of the leaves, and performs the same function as a tea infuser . Some tea bags have an attached piece of string with a paper label at the top that assists in removing the bag while also displaying the brand or variety of tea . </P> <P> In countries where the use of loose tea leaves is more prevalent, the term "tea bag" is commonly used to describe paper or foil packaging for loose leaves . They are usually square or rectangular envelopes with the brand name, flavour and decorative patterns printed on them . </P> <P> In China, during the Tang Dynasty (618--907), paper was folded and sewn into square bags to preserve the flavor of tea . </P>

When were tea bags first sold in the uk