Pillivuyt mugs and cups are made of fine French porcelain and are microwave, dishwasher and freezer safe. Each teacup, coffee mug and breakfast mug is fired at 2,400 degrees Fahrenheit. The high firing temperature creates cup and mug that is hard, nonporous and resistant to scratching and chipping. The glossy smooth glaze will not craze. What is really great about Pillivuyt mugs is how well they retain their heat, allowing your hot tea or coffee to stay hotter longer.