Contigo AUTOSEAL® technology guarantees 100% spill and leak poof drinking experience by sealing automatically between sips: press gently to drink and release to seal. The West Loop drinking mugs use vacuum-insulated technology, keeping hot drinks hot for up to 4 hours and cold beverages cool for up to 12 hours. The lid flexes open for easy cleaning and there are no loose parts.   Autoseal® Automatically seals between sips to ensure no spills. Press to sip. Release to seal One-handed operation Double-wall stainless steel Lid is dishwasher safe   We say - granted these are a little more expensive than other travel mugs but they are by far the best in the market. They never drip, never spill and they really do keep your drink warm. We can't recommend them highly enough.