This thermal mug has an integrated filter in the lid. This offers you two ways of preparing tea. You can either fill loose tea and hot water directly into the mug and use the lid as a filter. Alternatively, you can put loose tea in the lid and hot water in the mug. Then turn the closed mug upside down for the brewing process to start. Stainless steel is a high-quality, non-rusting material that is easy to clean.