Any tumbler that's coming along for the ride needs to be tough enough to keep up. The Yeti Rambler 20 oz (591 ml) is made from durable stainless steel with double-wall vacuum insulation to protect your hot or cold beverage at all costs. Fits in most cupholders. 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.