Type I Low Index (1.5 IOR)
The TT-B-1325D, Type I low index beads have been used on highways for decades, and were adopted by the FAA and USAF in the mid 90s for use on airports. Made from recycled glass,compared to the other approved bead types, Type I have the smallest diameter.Federal Specification TTB-1325,
Type II – is obsolete Federal Specification TTB-1325.
Type III (1.9 IOR)
Type III glass beads are made from virgin materials, not recycled glass and have an index of refraction (IOR) of 1.9 or higher
Type IV Low Index (1.5IOR), Type A and B
TT-B-1325C, Type IV “big beads” were approved for use by the airport industry in 2005. Also made from recycled glass or “direct hot melt”, they are larger than any of the specified glass beads. When applied in standard white waterborne paint, the reflectivity readings should range between 350-500mcd/m²/lux at installation. However, given the size of the glass bead (0.84 mm to 1.68 mm for TypeA, and 0.59 mm to 1.19 mm for Type B), they are best suited for use in the high build acrylic binder with a specified wet film thickness of at least 25-30 mils (TT-P-1952E, Type III). When Type IV glass beads are applied to standard water-borne traffic paint at 15 mils wet film thickness, results are poor. Type IV glass beads are applied using eight pounds per gallon of water-borne or solvent-borne paint.