zarf          
noun [ C ] uk/zɑːf/ us/zɑːrf/
 (热饮杯的)防烫环形圈
a tube-shaped piece of material that is put around a cup for hot drinks, to stop you burning your fingers when you hold it
  Did you know the cardboard thingy around a coffee cup is called a zarf? 你知道咖啡杯的一圈薄纸板叫“zarf”吗? 
 Synonym: cup sleeve
  (用以承托热饮杯的)装饰性金属杯形托
a decorative object made of metal and with a handle, used for holding a cup for hot drinks 
  Because the liquid is so hot, the cup is then placed into a decorative holder called a zarf. 因为热饮太烫,杯子会被放进一个叫“zarf”的装饰性杯形托里。 
 - More examples
 - I just found out that the cardboard sleeve on a coffee cup is called a zarf.
 - You need a zarf for a cup of coffee that's as hot as that.
 - I wish I had a few zarfs to put my coffee cups in.
 - Traditional tea and coffee cups without handles may have zarfs made of ornamental metal.