NS Novelties. Firefly Glass Butt Plug dreamy, playful and functional. Seductive and enticing, these glow in the dark little wonders are your ticket for endless fun when the sun goes down. Made of superior quality borosilicate glass with proven shapes designed to perform. Available in assorted sizes and suitable for all lubricants. Turn off the lights and turn on the fun. Product dimensions 3.1 inches by 1.5 inches by 1.5 inches.