Zojirushi stainless steel mug features Vacuum insulation that keeps beverages hot or cold for hours. The stopper disassembles for thorough cleaning. 2-Step lid release process prevents excess condensation on the stopper from being flung off while the lid opens. The air vent on the mouthpiece allows beverages to flow out smoothly, without gushing or overflowing. Tight fitted flip-open lid keeps beverages hotter or colder. Safety lock to prevent the lid from opening accidentally. Made of BPA-free plastic and stainless steel. Easy-to-clean nonstick interior. A special manufacturing technique was used to make the body ultra-lightweight and compact. 1-1/2" (4cm) wide mouth opening .