I used three different colored yarns together to make this bulky heart coaster. Two #3 light weight yarn and one #4 worsted weight yarn with a 5mm H hook. You can play around with the hook size depending on your yarn thickness. This heart coaster is a really quick project, taking around 15-20 min to make. 

NOTE: I read online that it is best to use "cotton" yarn for coasters, as "acrylic" yarn may melt when coming in contact with objects at high temperatures.