The Pope & Young branded Rambler 20 oz Tumbler with Magslide Lid is made from durable stainless steel so they are puncture and rust resistant. The double-wall vacuum insulation keeps your cold drinks cold and your hot drinks hot. Like the entire Rambler® Drinkware Family, the 20 oz. Tumbler and MagSlider™ Lid are dishwasher-safe for easy cleaning. 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, please note - this magnet component is not leakproof and will not prevent spills.