Many mugs are made of ceramic materials such as earthenware, bone china, porcelain or stoneware. Some are made from strengthened glass, such as Pyrex. Other materials, including plastic, steel and enameled metal are used where break resistance is at a premium, such as for campers. Techniques such as silk screen printing or decals can be used to apply decorations; these are fired onto the mug to ensure permanence.
A travel mug is a variation on the traditional mug that is better for transporting hot liquids. It may or may not be a vacuum flask, but is usually well insulated and completely enclosed, with an easily closed opening on the top.
