The entire Crystal line is made of 100% hand blown, premium Borosilicate glass, featuring the highest quality, most vibrant and durable glass products available today. Can be heated or cooled to personal preference. The NS Novelties Crystal Glass Eggs are made from 100% Borosilicate glass. Designed to bring pleasure to PC muscle exercise. Once inserted, they will help strengthen the Kegel muscle while providing rippling effects of stimulation throughout. A delicious yet discreet item, 1.75 inches by 1 inch. Includes a silk storage bag and a detailed instruction manual outlining PC muscle exercises designed to give pleasure and maintain a health muscle control.