Solid glass ben wa balls with ultra hygienic silicone strap Silicone strap makes them easy to insert and remove Silicone can be boiled, frozen, microwaved or placed on the top rack of the dishwasher Silicone’s soft texture becomes slick when lubricated Silicone is durable, nonporous, hygienic and can last a lifetime Waterproof Phthalate free