From the manufacturer:
These acid-free chalk-based pastels are ideal for students and aspiring artists. Made with pure pigment, they lay down color smoothly, without interruption, with excellent color opacity and good lightfastness. They possess good blending characteristics for rich pastel effects. Once a piece is finished, a gentle fixative is recommended. These sets feature half-length square sticks that measure 1-1/4" x 5/16" (24 pc set) and full-length sticks that measure 2-1/2" x 5/16" (12 pc set). Archival quality.