You just need to place the silicone cup cap over the glass or cup and enter the straw through the eyelet provided which will make your virtual spill proof container ready. It is made using antimicrobial silicone which makes this product strong, easy to wash and can be used again and again. It is sold in pack of two, out of which is 80 mm in diameter and other 60 mm. You can also use this cup cap to keep drinks fresh for longer time in the refrigerator. This pack contains 6 cm and 8 cm diameter cup caps.