Powder Materials FAQ

Hexagonal boron nitride is a multifunctional platy powder: it delivers lubricity, press strength, lustre and thermal conductivity at the same time, which is hard to replicate with a single alternative.

The platelet structure gives a low friction coefficient, so it feels silky rather than greasy. The platelets interlock during pressing and provide compact strength. Its refractive index and platy habit produce a soft satin lustre rather than the sparkle of mica. Thermal conductivity adds a slight cooling sensation on skin and helps the bulk dissipate heat.

Typical levels: 3-8% in pressed and loose powders, 5-10% in lipstick, 2-5% in liquid foundation. Above about 10% the lustre becomes pronounced, so use it sparingly in matte formulas.

The difference is shape and porosity, and that directly determines oil absorption, skin feel and optical behaviour. Regular silica consists of irregular particles and agglomerates; spherical silica is truly spherical, and porous grades carry interconnected internal channels.

The spherical shape gives a ball-bearing effect: particles roll over each other instead of interlocking, so the feel is smoother and spreading is easier. Porosity delivers high oil absorption, mopping up sebum and reducing shine, while the pores scatter light for a soft-focus effect.

The trade-off is that porous grades absorb formula oil as well. In low-oil systems, over-dosing can dry out the bulk or even break the emulsion. Keep levels at 2-5%, with somewhat higher levels acceptable in oil-rich formulas.

Bismuth oxychloride was once the workhorse for pearlescent effects, with strong lustre and good coverage, but photostability is its unavoidable weakness: it darkens and greys under UV and strong light, so products containing it often show shade drift over shelf life, especially in pale shades.

The usual replacement is synthetic fluorphlogopite or mica-based pearlescent pigments, which are slightly softer in lustre but far more stable. If the strong bismuth lustre must be kept, restrict it to packaging areas that are not light-exposed and validate photostability thoroughly.

Not on an equal-weight basis. Their functional profiles differ: mica is platy and provides lustre and adhesion, while talc is platy but softer, providing slip and oil absorption with weaker coverage.

Replacing talc with mica reduces slip and increases lustre, often making the formula look sparkly. Replacing mica with talc flattens the finish noticeably.

Also note that talc carries higher regulatory sensitivity because of the asbestos risk. Cosmetic-grade talc must be confirmed asbestos-free, which is one reason many export formulas proactively reduce talc levels. When replacing talc with mica, determine the approximate ratio experimentally, then fine-tune against the skin feel and lustre you need.

The core difference is platelet integrity and aspect ratio. Wet delamination cleaves along the platelet planes in a liquid medium, causing little damage and yielding a high aspect ratio. Dry milling relies on mechanical shear, which is efficient but fractures platelets and creates fines and debris.

In use, wet-delaminated boron nitride, talc and mica have thinner, more intact platelets, giving clearer lustre, better adhesion and more efficient coverage and soft focus at the same dose. Dry-milled grades scatter light more diffusely and feel rougher.

The cost gap comes from yield and process complexity. For premium pressed powders and lipsticks where lustre and adhesion matter, wet-delaminated grades usually deliver better value.

Choose based on the continuous phase: water-in-oil, oil-in-water, or anhydrous. Surface treatment exists to make the powder compatible with that phase.

Triethoxycaprylylsilane suits water-in-oil and anhydrous systems; treated powder becomes lipophilic and hydrophobic with good dispersion and a clean feel, which is why it dominates colour cosmetics. Polydimethylsiloxane treatment leans toward slip and water resistance, useful for transfer-resistant formulas. Stearic acid is inexpensive and lipophilic but has limited heat and shear resistance, so it can desorb during high-temperature processing or high-shear dispersion.

In practice, check the continuous phase first and the process temperature second. If processing exceeds 80 C, stearic acid treatments are effectively off the table.

Oil absorption is measured to GB/T 5211.15 or ISO 787-5: oil is added dropwise to the powder and worked in until the paste can be lifted as a single mass without sticking to the plate. The result is expressed as grams of oil per 100 g of powder.

The number is neither good nor bad on its own — it depends what you need. High values (porous silica, kaolin) mean the powder absorbs sebum and delivers matte, soft-focus results, which is what oil-control formulas want. Low values (treated talc, mica, boron nitride) mean the powder will not steal oil from your formula, so the cream stays emollient and stable.

Two practical caveats. Different test oils give different numbers — linseed oil versus DOP can differ by 10-20%, so confirm the oil type before comparing datasheets across suppliers. And oil absorption is a static figure: what actually drives skin feel is the absorption rate, which surface treatment can cut substantially without changing the endpoint. Two powders with identical oil absorption can feel completely different. Our COA states both the standard and the oil type used.

Broadly positively correlated, but not linear, and porous grades deviate most.

BET specific surface area measures the total accessible area including pore walls; oil absorption measures how much oil those surfaces can hold. Larger area and accessible pore volume generally mean higher oil absorption. Fumed silica at around 200 m²/g can exceed 300 ml/100 g, while ground calcium carbonate below 5 m²/g sits at 15-20.

The correlation breaks down in two cases. First, closed porosity: some porous powders show a large surface area but the pore openings are too narrow for larger oil molecules to enter, so real oil absorption stays low. Second, surface treatment: silane or silicone coating occupies part of the surface, dropping BET by 10-30% while reducing absorption and absorption rate even more.

So never select on one number. Oil absorption answers oil control, surface area answers dispersion and reinforcement, and surface treatment answers skin feel — three different questions.

Whiteness and coverage follow different curves: coverage depends on refractive index contrast, whiteness on reflectance. Titanium dioxide maxes out both at once, so the problem is rarely not white enough — it is too white.

TiO2 has a refractive index around 2.6, the highest of any common cosmetic powder, and 3-5% already delivers ample coverage. Above 8% you hit three problems: the finish turns chalky and loses translucency, which is very visible in pressed and loose powders; spreadability drops and application feels draggy; and cost climbs while coverage has already plateaued.

A layered approach works best: TiO2 for coverage at 3-5%, calcined kaolin or talc for bulking and cost, mica or boron nitride for translucency and luminosity, plus iron oxides for hue adjustment. If you want white with depth rather than white like flour, either move part of the TiO2 to a surface-treated grade or use a coarser rutile grade at D50 200-300 nm — similar coverage efficiency, noticeably better translucency.

Mica gloss comes from specular reflection off its platelets. The larger and more intact the platelet, the larger each reflective surface and the more sparkle; finer grades read as a soft silky sheen.

Three practical bands. D50 10-20 μm gives soft luster, low coverage and good adhesion, ideal for loose and pressed powders where you want satin rather than shine. D50 20-40 μm balances gloss and coverage and is the general-purpose choice for foundations and pressed powders, and the usual substrate for pearlescent pigments. Above D50 40 μm reflection is strong and visibly sparkly, good for eyeshadow and highlighters, but high loadings emphasize pores.

Two technical points matter more than the headline D50. First, aspect ratio beats particle size: wet-ground mica has intact platelets and a high aspect ratio, so at the same D50 its luster is more transparent, while dry-milled mica scatters light and looks flatter. Second, surface treatment: mica is hydrophilic and settles readily in oil systems, and silane or titanate treatment improves both adhesion and dispersion.

For pearlescent effects, remember mica is only the substrate — the interference color comes from coating thickness, so ask your supplier for the specific interference shade rather than guessing from the substrate grade.