For the Sure Grip Mug. 
  
The specially designed drinking lids are a perfect fit for the Sure Grip mug – the valve in the lid prevents leakage if the mug i tipped over. You can comfortably drink (suck) lying down. You have complete control over the flow of the liquid.
 
The lid comes with a small aperture for thin liquids, or a large aperture for thick liquids/food

More Information:

The Drinking lid are also available in heat sensitive plastics. It means tha the lid changes color when the contents are too hot.The lid changes color when the liquid is above 28 degrees Celsius.

The deep purple colour indicates that the liquid in the mug is below 38 degrees celcius.	The liquid is below 38 degrees celcius and is ready for consumption.	The liquid is more than 38 degrees Celsius and is too hot for consumption.