The planet waves glass slides are made from boron silicate for enhanced durability, smoothness and tone. each slide is individually heat treated to provide smooth edges and a perfect finish allowing the slide to glide over strings while the 4mm glass thickness produces a warm, thick tone. the slides are available in small, medium and large sizes. bull; flawless finish and extra smooth surface glides over strings bull; nbsp; 4mm wall thickness produces warm, thick tone bull; nbsp; available in small, medium and large sizes