The Rambler 10 oz Stackable Mug is made from durable stainless steel with double-wall vacuum insulation to protect your hot or cold beverage at all costs. While the MagSlider Lid adds a barrier of protection for keeping drinks contained and preventing heat or cold from escaping, Please Note ? The MagSlider Lid is not leakproof and will not prevent spills. YETI Ramblers are BPA-free, dishwasher safe, and have a No Sweat Design to make sure your hands stay dry.