[Freezer-Friendly] This mug can also be used in the freezer if you want to keep your drink cold. [Keep Hot or Cold] Each mug holds 300 ml, double-layered! Keeps drinks hot for up to 2 hours and cold for up to 6 hours. [Twist-On No-Lid Design] This new mug features a silicone membrane and a revolutionary no-lid design. Instead, you simply twist the silicone membrane onto the top of the mug and watch a seal form. [Easy to Use] This mug is super easy to use, just twist the top film and watch a seal quickly form on the top of the mug. [Leak-Proof] The silicone membrane is adjustable, leaving enough room for a straw to pass through the top. Simply place a straw into the opening and twist the membrane until the straw fits snugly in place. With the new seal, liquid 't fall out of the mug.