Vacuum insulation provides superior heat retention--your beverage stays hot or cold for hours. A special manufacturing technique was used to make the body ultra-lightweight and compact. Zojirushi flip-open lids are designed to release and hold, then flip open. This 2-step lid release allows condensation on the lid gasket to fall back into the mug instead of splattering. Lid completely disassembles for easy and thorough cleaning. Air vent on the mouthpiece allows beverages to flow out smoothly, without gushing or overflowing. Safety lock prevents the lid from opening accidentally. Nonstick coated interior makes cleaning easy. 2.5cm - 1.6cm wide opening for easy filling. Vacuum means the air between the outer and inner layers of stainless steel has been removed to create a vacuum insulation. It blocks heat from transferring through air (conduction). Zojirushi vacuum insulation also features a copper or aluminium layer tightly wrapped around the outside of the inner stainless steel layer. This copper or aluminium layer reflects heat (radiation), further minimising the temperature change of your drink. Lastly, heat is blocked from escaping through the opening (convection) with a tightly closed lid. Zojirushi was established in 1918 as a producer of hand-blown vacuum bottles. The Zojirushi line was expanded to include a wide range of stainless steel vacuum bottles, rice cookers, breadmakers, Air Pot beverage dispensers, thermal serving carafes, specialty cookware, small electrics, restaurant equipment and other products. Striving to remain faithful to the principles that embodied the company's first 100 years, and the reputation of quality and durability it earned them, Zojirushi looks forward to a future of continued innovation and inspired design.