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Two jobs, two classes

Retroreflection works like this: headlight beams enter the exposed crown of a bead sitting in the line, refract inside the glass, reflect off the bead–paint interface and return toward the driver. BS 6088 splits beads by where they sit in that system:

The two road classes pair with the British thermoplastic standard: BS 3262 calls for premix beads to BS 6088 Class A when the line must reflectorize, with Class B dropped on during application. The classes are not interchangeable — A is deliberately coarser and lives inside the material; B is sized to embed about half-deep in the surface.

Class B gradation — Table 2 of the standard

The working range is 180–850 μm with the bulk at 300–600 μm — big enough to sit proud of the coating and form a reflecting crown, small enough to embed and stay put. Note the table is written as retained per sieve, not cumulative passing: the two formats give completely different numbers, and misreading one as the other is the most common mistake when auditing a datasheet. For comparison, the premix grade (Class A, Table 1) runs coarser: 0–3% retained at 1.18 mm, 5–20% at 850 μm, 65–95% at 425 μm, 0–10% passing 425 μm.

Bead quality — beyond the sieve

Drop-on roundness is set tighter than premix because the sphere shape of a surface bead directly drives the initial night-time brightness. Defective beads — ovals, twins, shards, milky or bubbled glass — are counted under the microscope. The standard also proves durability with four chemical-resistance tests: water, acid and calcium chloride exposure must leave the bead surface without haze or dulling, and a sodium sulphide bath must not darken the beads — a simple screen against high-lead recycled glass, which turns black on contact.

Coatings, and how to order

Class B beads can carry two buyer-specified surface treatments: M, a moisture-proof coating that keeps the beads free-flowing through the dispenser in humid transit and storage, and F, a flotation coating that helps the bead sit at the right depth in the wet coating. A complete order code reads “BS 6088 Class B (M)” or “(M+F)”. A clean tender clause looks like this:

“Glass beads shall conform to BS 6088:1981 Class B, with moisture-proof coating (M); roundness ≥ 80%; refractive index ≥ 1.5; gradation as per Table 2 of the standard.”

In practice, hot-applied thermoplastic takes a drop-on rate around 400–500 g/m² and cold paint 250–450 g/m², with the bead embedded 50–60% of its diameter for best return — useful working figures, but they are industry practice, not clauses of BS 6088, so state your project’s own rate in the contract.

BS 6088B, EN 1423, AASHTO M247 — which to cite

The BS 6088B band (180–850 μm) overlaps closely with M247 Type 1 — they are effectively the British and American write-ups of the same size class, with BS 6088B holding the stricter roundness. One caution for 2026 contracts: AASHTO revised the bead standard to M 247-26, so name the year rather than writing “latest M 247”. EU or UK projects should be quoted against EN 1423 instead — the same product can satisfy both, but the paperwork differs. Tell us which code your tender cites and we quote against that text.