This Dunlop 202 Glass Slide offers a warmer, thicker tone accentuating the middle harmonics of your sound. Processed from high quality boron silicate. Heat treated and annealed for a flawless tube. Tempered glass guitar slides are preferred for full, rich tones. They sound warmer and more resonant than metal slides, producing smooth transitions with minimal string noise. Tempered glass slides are the top choice for many acoustic players, and they're also favored by electric players who want the purest slide tones possible.