Stainless steel vacuum insulation keeps beverages hot or cold for hours; Heat retention: 181°F @ 1 hr. / 135 °F @ 6 hrs.; Cold retention: 50°F @ 6 hrs. Easy-to-clean nonstick coated interior Rounded sip area, designed to drink directly out of the mug A special manufacturing technique was used to make the body ultra-lightweight and compact 1-5/8” (4cm) wide mouth opening