A Go-To Coffee On The Go. Fits In Most Cupholders Any tumbler that's coming along for the ride needs to be tough enough to keep up. Our fan-favourite Rambler® 20 Oz ( 591 ml). Tumbler is made from durable stainless steel with double-wall vacuum insulation to protect the temp of your beverage at all costs. Like the entire Rambler® Drinkware Family, the 20 Oz ( 591 ml). 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.