In solventborne systems, almost any precipitated silica will kill gloss. Waterborne wood coatings are far less forgiving: the resin is a dispersed polymer, viscosity is low, film formation depends on coalescence, and factories in Southeast Asia routinely run at 80–90% relative humidity. Choosing a matting agent here comes down to three parameters on the datasheet — and how honestly they match your film.
1. Particle size (d50): the gloss–clarity–touch triangle
Median particle size is the first and most powerful lever.
- Too fine (well below the dry-film thickness): particles sit inside the film instead of texturing the surface — matting efficiency drops and you over-dose to compensate, driving viscosity up.
- Too coarse (far above the dry film): strong matting, but the surface turns rough, hand-feel suffers, and on dark solid wood you see grey "grain" and haze.
- The working rule: d50 should sit at, or slightly above, the dry-film thickness. For a typical 20–40 μm waterborne clear topcoat, a narrow 5–6 μm grade is the sweet spot; deep-matte tactile finishes move up to 6–6.5 μm.
Just as important as the median is the width of the distribution. Two grades can share a d50 of 5 μm, but the one with a long coarse tail will scatter light unevenly — that is the difference between "matte and water-white" and "matte but slightly milky" on dark substrates. This is why narrow-PSD grades such as Censil660 (5.0–5.3 μm) are specified for high-clarity work.
2. Pore volume: matting efficiency vs. viscosity
Pore volume (typically 1.6–1.8 mL/g for coating-grade silica) determines how much surface roughness each gram of silica creates — and how much liquid it absorbs.
- Higher pore volume = more matting per gram, so lower dosage. But it also means more binder absorption, which raises viscosity and can embrittle thin films.
- Lower pore volume = gentler on rheology, but you dose more to reach the same gloss, which hurts transparency.
For waterborne wood systems, a balanced 1.6–1.8 mL/g grade at a 1–4% dosage on total formulation normally reaches 10–30 GU (60°) without destabilizing viscosity. If you need more than ~5% to hit target gloss, the grade is wrong — don't push the dosage.
3. Surface treatment: the difference between a powder and a product
Untreated hydrophilic silica works — until the can sits in a warehouse for a month. In low-viscosity waterborne systems, untreated particles settle and pack into a hard cake that never redisperses. Surface treatment with high-melt PE wax changes three things:
- Soft settling. Wax-coated particles form a loose, stir-back sediment instead of a hard cake.
- Touch. The wax layer gives the cured film a smoother, silkier hand-feel and better burnish resistance — critical for furniture.
- Humidity behaviour. The hydrophobic shell reduces water pickup at the film surface, which is a major factor in whiting at 80%+ humidity.
For clear topcoats and anything sold into Vietnam or Malaysia's climate, specify a wax-modified grade. Pair it with a small addition of fumed silica for thixotropy and the anti-settling package is complete.
Putting it together: a quick selection map
| Target finish | System | d50 guide | Censil grade | Import benchmark |
|---|---|---|---|---|
| High-clarity water-white matte | WB clear topcoat (acrylic/PUD/UV) | 5.0–5.3 μm | Censil660 | SYLOID® ED 30 |
| Fine semi-matte, smooth touch | WB high-clarity clears | 4.9–5.2 μm | Censil651 | SYLOID® ED 2 |
| Universal semi-matte / matte | WB wood & industrial | 5.9–6.2 μm | Censil361C | SYLOID® ED 4 |
| Deep-matte tactile | WB furniture / plastic | 6.2–6.5 μm | Censil1650A | SYLOID® ED 30 |
A 30-minute evaluation protocol
- Prepare a dosage ladder at 1%, 2%, 3%, 4% in your production formulation (high-speed dispersion, 15–20 min, no grinding needed).
- Draw down on glass and on a dark-stained wood panel at your production wet-film thickness.
- Measure 60° gloss; judge transparency and grey-cast on the dark panel; assess touch after full cure.
- Run a 7-day 50°C storage test on the matted paint — check for hard sediment and viscosity drift.
The dark-panel and storage steps are where cheap silica fails and where a properly engineered grade earns its price. See the full grade table and physicochemical data, or read common problems and fixes if you're diagnosing an existing formulation.
Dosage: the variable that quietly undoes a good grade choice
Particle size and pore volume decide what a grade can do; dosage decides what it actually does in your can. Matting is a surface-crowding effect, so the relationship between loading and gloss is non-linear — the first increments of silica drop gloss quickly, then the curve flattens as the film surface saturates. Two consequences follow. First, build a dosage ladder rather than betting on a single point; the useful working window is often narrower than the datasheet range. Second, the same target gloss can be reached either with a small dose of a high-efficiency (high pore volume) grade or a larger dose of a coarser one, and those two routes give different clarity, viscosity and cost per litre. Picking a grade without fixing a dosage window is answering only half the question.
Why gloss is a geometry problem, not a bulk one
Gloss meters read specular reflection at a fixed angle — 20° for high-gloss, 60° for semi-matte, 85° for the sheen of low-gloss films. A matting agent works by pushing micron-scale roughness to the very top of the dried film, scattering that specular beam. This is why film thickness and drying conditions matter as much as the silica itself: a thicker wet film buries particles and raises gloss, while fast forced-drying can lock in a rougher surface and lower it. When you compare two grades, hold wet-film thickness, substrate and drying schedule identical — otherwise you are measuring your process, not the additive.
Five selection mistakes that cost a reformulation
- Buying on d50 alone. Two grades with the same median particle size but different pore structure and surface treatment behave differently in the same binder.
- Ignoring the binder. A grade optimised for a self-crosslinking acrylic can settle or haze in a polyurethane dispersion. Match the grade to the resin chemistry, not just to the end application.
- Over-loading for “deep matte.” Past the saturation point you gain little further gloss reduction and start trading away clarity, burnish resistance and film integrity.
- Testing only on white charts. Haze and grey-cast only reveal themselves on dark substrates; a grade that looks flawless on an opacity chart can turn a black-stained panel milky.
- Skipping the storage test. A grade that performs on day one but hard-packs after four weeks in a warm warehouse has not passed evaluation.
Waterborne is not solventborne: the treatment has to match the carrier
Surface treatment is not universal. A wax-treated or organically treated silica designed for a solventborne furniture lacquer can disperse poorly, float or seed in a waterborne system, because wetting and re-agglomeration behave differently in water than in solvent. When you shortlist a grade for a waterborne wood or plastic coating, confirm the treatment is specified for aqueous systems. This one check prevents the most common evaluation failure — “the sample looked fine on the drawdown but the production batch seeded.”
Read the datasheet critically before you shortlist
A matting-agent datasheet gives you comparable numbers only if you know what each one drives. Median particle size (d50) sets the gloss–clarity–touch balance; the distribution around it governs haze and the risk of visible seeds. Pore volume signals matting efficiency per unit dose but also warns of viscosity build. The surface-treatment line tells you whether the grade is engineered for waterborne or solventborne carriers, and whether it adds burnish or scratch resistance. Bulk density and residual moisture matter for dosing and storage. Treat any single number in isolation with suspicion: a grade is a system, and the datasheet is only useful when you read the four or five properties together against your own film and process.
Anchor every choice to a gloss target and end-use
Before comparing grades, write down the finish you actually need — a 60° gloss band, the substrate colour, and the durability the end-use demands — because the “best” grade is meaningless without that target. A dead-matte dark furniture topcoat, a soft-touch plastic housing and a low-sheen clear over pale wood have different tolerances for haze, burnish and dosage, and they rarely land on the same grade. Fixing the target first turns grade selection from an open-ended search into a short, testable shortlist, and it gives you an objective pass/fail line for the 30-minute evaluation above.