The refractive index (RI) is a function of the chemical makeup of the beads, which is determined by the raw material used to make the bead. The higher the refractive index, the more light is retroreflected. Refractive index is tested by using Test Method .

Most beads used in roadway striping nationwide have a refractive index of 1.50. A bead with a 1.50 refractive index is made from recycled windowpane glass. Beads with higher refractive indices, including 1.65 and 1.90, are made from virgin glass and have a different chemical makeup. Higher refractive index beads are not frequently used because they are more expensive and may be slightly less durable than 1.50 RI beads. Some agencies use a blend of higher and lower refractive index beads.