These luxurious black Ben Wa balls are made from borosilicate glass and designed to last a lifetime. Their size and weight make them perfect for vaginal stimulation and exercise use, and the nonporous glass is hypoallergenic and body safe. With regular use, you will enjoy improved muscle control and stronger, more frequent orgasms. Run them under warm water or place them in the microwave to heat things up. Chill them under cold water or put them in the freezer for a cool sensation.