20 oz. is made from durable stainless steel with double-wall vacuum insulation to protect your hot or cold beverage at all costs. The 20 oz. Tumbler and its 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.