The Yeti Rambler MagSlider (295 ml) insulated wine tumbler with magnetic lid is made of stainless steel, well appreciated on the pool deck or while camping, when we need to ensure nobody gets hurt by broken glass. While the magnet on the included MagSlider™ lid adds an additional barrier of protection for keeping drinks contained and preventing heat or cold from escaping, note that this magnet component is not leakproof and will not prevent spills.