These mugs or cups with lids act as a one person teapot. Just add tea to the inclusive filter and remove it when the tea is brewed. In a non-lidded mug many of the finely flavoured volatile oils disappear in the steam and the water cannot stay hot enough to properly extract all the essential ingredients from the leaves. Effectively you have your own one stop teapot. You can also enjoy the water changing colour as the tea flavour and colour starts to swirl out. They will even make a tea bag taste better!