This mug features a groundbreaking advancement in thermal insulation. Sea to Summit use an integrated molded EVA sleeve that actually insulates the liquid inside the mug, unlike double-walled mugs which only protect your hands but don't necessarily keep your beverages hot or cold. Well designed leak-proof sipping lid has an ergonomic rolled edge and thumb grip with hang loop. Excess liquid flows back into the sipping hole because of the concave design of the lid.