The stylish Ichimatsu Collection mugs are equipped with high quality double wall stainless steel vacuum insulation construction that keeps beverages hot or cold for hours. The tight-fitting flip-open lid with safety lock makes drinking from the mug easy, and prevents beverages from spilling. 2-step lid release process prevents excess condensation on the stopper from being flung off while the lid opens. Tight-fitted flip-open lid keeps beverages hot or cold. Safety lock to prevent the lid from opening accidentally. A special manufacturing technique was used to round the bottle opening, making it smooth and comfortable to the touch when cleaning. 1-5/8" (4cm) wide mouth opening. Easy-to-clean double layer nonstick coated interior enhances durability, and provides greater protection of the stainless steel against salt-containing beverages like sports drinks. Made of BPA-free plastic and 18/8 stainless steel. The lids are interchangeable with SM-NAE48, allowing for a wide choice of color combinations and use. "Ichimatsu" is a two-toned checkerboard pattern that holds historical significance and recognition in Japanese culture. In the mid-Edo period, a popular Kabuki actor named Sanogawa Ichimatsu was known for wearing pants with this pattern.