This lid fits onot a typical disposable cup that you get get at airporst and other drinks outlets. The lid is manufactured with a temperatura-sensitive additive. Before the lid is put onto the cup, it is coffee-coloured. When the lid heats up, the additive changes colour and the lid turns red; the user is warned to be careful of the hot liquid. When the drink coosl., the colour of the lid changes back to brown. The Smarn Lid has another excellent feature. When it is put on correctly, this ring is incomplete. This gives the user an sdditiional warning that the hot liquid could spill out of the cup.