Thermos Stainless Steel Vacuum Insulated Flask with Screw Stopper 350ml Midnight Blue is engineered with double-wall vacuum insulation to keep beverages hot for hours or refreshingly cold throughout the day. The precision screw stopper minimizes heat transfer while helping prevent leaks during transport. Manufactured from durable stainless steel, the lightweight flask is ideal for commuting, school, travel, and outdoor activities. Preheat or pre-cool before filling for maximum thermal efficiency and wash by hand after use.