Ask a buyer what bead they need and the answer usually arrives as a mesh number. Ask which marking system the beads are going into and the conversation tends to stall. That is the wrong way round. Film thickness, application temperature, cure speed and the speed of the applicator all constrain the bead before a single sieve number becomes relevant.
This is a guide to selecting glass beads by marking system, using the groupings that GB/T 24722-2020 already recognises and the field parameters that decide whether a bead stays where it is put.
The marking system decides the bead
A drop-on bead has a few seconds to anchor itself in a hot film and then spend years being driven over. Its size, its coating and the dosage all have to be matched to the surface it lands on. A thermoplastic line applied at 2 mm can swallow a coarse bead; a waterborne paint film measured in fractions of a millimetre cannot, and a bead that cannot embed will be thrown off by traffic within weeks.
Four variables do the constraining, and they move together:
- Application temperature — how much the film can soften around a bead, and how fast it sets afterwards.
- Wet film thickness — the physical space a bead has to sink into.
- Open time before cure — the window during which a bead must be applied and settle.
- Application speed and method — whether beads can come to rest or are dragged through a liquid film.
GB/T 24722-2020 already maps beads to systems
The Chinese national standard for pavement marking glass beads does not leave the pairing to guesswork. It defines four types by the job each one performs.
| Type | Intended job (GB/T 24722-2020, 4.2) |
|---|---|
| 1 | Drop-on beads for thermoplastic, two-component and waterborne marking paints |
| 2 | Premix (internal) beads for thermoplastic and two-component paints |
| 3 | Drop-on beads for solvent-based paints |
| 4 | Wet-night beads, used together with non-wet-night beads as drop-on material |
Read down that table and two things stand out. Waterborne and solvent-based paints are deliberately separated into different drop-on types. And thermoplastic and two-component systems are the only two that take beads both ways — internally and on the surface. That pairing is where most of the specification argument happens, and the technical difference between drop-on and premix beads explains why the two sieve tables will not substitute for one another.
Thermoplastic: high heat, thick film, large beads welcome
Hot-applied thermoplastic is the most forgiving system for glass beads, because it offers heat, depth and time.
| Parameter | Practical range |
|---|---|
| Material temperature at application | Around 200°C; a common working band is 180–220°C, raised by 10–20°C in cold weather |
| Typical line thickness | 2.0 mm general; 2.0–2.5 mm in expressway designs; profiled rumble lines are much thicker |
| Drop-on window after application | 10–30 seconds, while the film is still semi-molten |
| Drop-on dosage | 0.3–0.45 kg/m² in common practice; high-performance, long-life designs may specify up to 0.6 kg/m² |
| Bead embedment target | 50%–60% of the bead diameter below the surface |
Temperature is the parameter that fails most often in both directions. Run the material too hot and it thins, beads sink past the effective depth and the line goes dull; run it too cold and the film is too viscous for beads to inset at all, so they sit loose on the surface and are swept away. Several municipal specifications handle this by requiring a trial strip, and by making the embedment depth a hard acceptance criterion rather than an aspiration.
Dosage is applied in two passes in many designs for a reason: a coarse fraction first, then a finer one. Two passes avoid the shadowing problem where large beads crowd out small ones, and they distribute coverage more evenly.
Two-component: the narrowest drop-on window
Two-component markings, whether methyl methacrylate or epoxy based, use the same bead types as thermoplastic but tolerate much less hesitation. The system cures chemically rather than by cooling, so the period in which a bead can still sink into the film is short, and it does not reopen if the applicator is slow.
The film build also differs. A common two-component construction applies a base coat by trowel at roughly 0.5–1.1 mm and a top coat by spray at 0.5–0.7 mm. That top layer is thin. It accepts fine and medium drop-on beads readily, and it will not accept a coarse bead that needs more than a millimetre of soft material to anchor in. Projects that ask for a big-bead, high-retroreflectivity finish on a two-component system are usually asking for something the film cannot deliver, and the discrepancy typically surfaces as a failed embedment check rather than a complaint about the beads.
Two-component systems do take premix beads as well, which is the more reliable route to a durable internal bead content when the top coat is thin: the beads are already distributed through the material instead of being landed on top of it.
Waterborne and solvent-based paint: thin films and the rolling-bead problem
Paint-based markings are the case where application technique starts to matter as much as the bead. Films are thin, and the material stays mobile for longer.
| Waterborne paint | Solvent-based paint | |
|---|---|---|
| Bead type specified by GB/T 24722-2020 | Type 1, drop-on | Type 3, drop-on |
| Water resistance limit | Neutralise no more than 10 mL of 0.01 mol/L hydrochloric acid | No more than 15 mL |
| Main risk | Beads rolling in a wet film rather than anchoring | Solvent attack on any bead surface coating |
| Dosage tendency | Typically higher relative to film than thermoplastic | Per project specification |
The rolling problem is well documented in American practice. In thin-film markings such as waterborne paint and epoxy, applying beads while the applicator is travelling faster than about 10 mph — roughly 16 km/h — causes beads to roll through the wet film and be swallowed by it, losing their retroreflective function entirely. The bead is not defective; it was simply given no opportunity to settle. This is one of the failures that looks like a bead problem and is not.
The other paint-specific detail is easy to overlook. Type 3 beads, intended for solvent-based paints, are held to a slightly looser water-resistance figure than types 1 and 2 precisely because they live in a different chemical environment. Specifying type 1 beads into a solvent-based system because the sieve size looked right is a common and avoidable error.
Wet-night and all-weather markings
Wet-night performance is a separate design decision, not an upgrade you get for free.
GB/T 24722-2020 defines type 4 beads as wet-night beads, intended to be used together with non-wet-night beads rather than on their own, as drop-on material for thermoplastic and two-component systems. The standard also grades beads by refractive index: low index from 1.50 up to 1.70, medium index from 1.70 to 1.90, and high index at 1.90 and above. For wet-night work the medium and high grades are the relevant ones, and the closer the refractive index sits to about 1.93, the stronger the return.
Two practical points follow. First, a high-index bead has a higher density, which changes how it settles in a given film and how it behaves in handling. Second, larger drop-on beads used for wet-night visibility are harder to embed than standard sizes, which is why American practice calls for an attachment or floating coating on the largest drop-on grade so that it holds its position in the film. The standard tests a moisture-resistant coating by whether beads pass through a funnel without stalling (5.8) — a small test that predicts whether the coating will still be doing its job on the road. Why glass beads decide whether a marking works at night covers the underlying optics if you need to argue the case for the upgrade.
Match bead size to film thickness, or nothing else matters
If you take one rule from this guide, take this one: a bead needs somewhere to embed, and the film has to be thick enough to provide it.
Thick markings can carry large beads; thin markings cannot. Put a coarse bead on a thin overlay and there is not enough material for it to sit in, so the exposed portion is too great, the bond is too small, and the bead leaves with the first traffic. The result is a marking that reads well on the day it is laid and poorly a month later — the pattern described in ten causes of marking bead failure, where embedment sits at the top of the list.
The target in normal practice is 50%–60% of the bead diameter below the surface, which leaves 40%–50% standing proud to catch and return light. American guidance is blunt about which way to err: if a mistake must be made, too deep is better than too shallow, because an under-embedded bead disappears quickly while an over-embedded one merely underperforms. There is an upper limit as well. Applying beads far beyond the specified dosage does not add brightness; beads pile up, shield each other and the pattern of repeated internal reflection that produces the return light breaks down.
A selection table for tenders
| Marking system | Bead type | Typical film | Drop-on dosage | What to watch |
|---|---|---|---|---|
| Thermoplastic, hot applied | 1 drop-on, plus 2 premix | 2.0–2.5 mm | 0.3–0.45 kg/m², frequently in two passes | Material temperature and embedment depth |
| Two-component | 1 drop-on, plus 2 premix | Base 0.5–1.1 mm, top 0.5–0.7 mm | Per project specification | Narrow open time before cure; thin top coat limits bead size |
| Waterborne paint | 1 drop-on | Thin film | Often higher relative to film than thermoplastic | Beads rolling if the applicator travels too fast |
| Solvent-based paint | 3 drop-on | Thin film | Per project specification | Solvent compatibility of any bead coating |
| Wet-night / all-weather | 4 together with non-wet-night beads | As the base system | As the base system | Higher density affects settling; large sizes need attachment coating |
Use the table to set the questions, not to skip them. It is a strong starting position for a tender, and a glass bead specification checklist for road marking projects turns it into the list of numbers a supplier should be asked to put in writing.
Where Linghang fits
Yongqing Linghang Glass Beads grades road marking beads to the sieve tables that different systems require, so the grade is chosen together with the system rather than after it. Drop-on grades for marking work are held across the common mesh ranges, and premix grades are cut to a customer’s own internal size requirement.
Two things a buyer usually wants confirmed before the first container. First, the documentation: test reports can be issued against GB/T 24722-2020, and where a project is specified to a different convention, results can be presented against the sieving logic of AASHTO M247 or EN 1423 so that a single lot serves both. Second, the difference the 2024 Chinese marking standard makes: because GB/T 16311-2024 now tests the finished marking for internal bead content, the properties of a premix or drop-on lot have to survive application, not just delivery. What GB/T 16311-2024 changed for bead buyers sets out the specifics.
Drop-on glass beads for road marking in 20/40 mesh, high clarity is one of the grades held for marking work. Tell us the system, the film thickness and the target retroreflectivity class, and we will match the grade and sieving to it.
