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Silicon dioxide

Silicon dioxide suppliers and sourcing guide

Silicon dioxide used in food and supplements is synthetic amorphous silica, a very light white powder. It is made either by burning silicon tetrachloride in a hydrogen-oxygen flame (fumed or pyrogenic silica) or by precipitating it from sodium silicate solution with acid (precipitated silica). Its large surface area lets it hold moisture and oils and keep particles apart. Brands use it as an anticaking agent, glidant and carrier for liquids in powders and tablets.

See suppliersWhat to ask for on the COA
Also known as
Silica · Colloidal silicon dioxide · Fumed silica · Precipitated silica · E551
Facts checked
November 2026

Forms and grades of silicon dioxide

Suppliers sell different products under the same name. Specify the one you need.

  • Fumed (colloidal) silica

    Pyrogenic silica with very fine primary particles and high surface area, the usual tablet and capsule glidant.

  • Precipitated silica

    Higher-density silica used as an anticaking agent and as a carrier that turns oils and liquids into free-flowing powders.

  • Hydrated silica

    Precipitated silica gels sold for oral care and food uses, with stated water content.

  • Natural source silica

    Silica from bamboo or rice hulls, sold mainly for organic or label reasons.

What to check on the COA

Compare each result with your own specification when the lot arrives.

Assay
SiO2 content on the ignited basis, by gravimetry after hydrofluoric acid treatment as in the pharmacopeial and FCC methods.
Loss on drying and loss on ignition
Moisture and bound water, which differ between fumed and precipitated grades.
Specific surface area
BET surface area, the main functional specification.
pH and soluble salts
pH of a suspension and residual sodium sulfate or chloride for precipitated grades.
Heavy metals
Lead, arsenic and other metals by ICP-MS against the specification.
Particle size and tapped density
Particle size distribution and tapped density, which affect dusting and flow.

Storage, lots and expiry

Storage and shelf life

Keep in sealed bags or containers in a dry place; silica readily adsorbs moisture and odors from the air, which reduces its capacity as a flow agent. The powder is extremely light and dusty, so open and dispense it with dust extraction. Shelf life or retest dates come from the supplier, often several years, with loss on drying retested.

Lots and expiry dates

Surface area, moisture and tapped density vary by lot and between fumed and precipitated types, and they change flow and how much liquid the silica can carry. Record the grade, surface area and loss on drying per lot.

Regulatory status

Facts from regulators and standards bodies, each linked to its source.

  • 21 CFR 172.480 permits silicon dioxide as an anticaking agent in food in an amount not to exceed 2 percent by weight of the food.

    Source: ecfr.gov (opens in a new tab)

  • 7 CFR 205.605 lists silicon dioxide among the synthetic substances allowed in organic products, permitted as a defoamer and allowed for other uses when organic rice hulls are not commercially available.

    Source: ecfr.gov (opens in a new tab)

  • Health Canada's List of Permitted Anticaking Agents allows silicon dioxide as an anticaking agent in listed foods, including foods sold in tablet form.

    Source: canada.ca (opens in a new tab)

This is general information, not regulatory advice. Status differs by country and by how the ingredient is used, so check the rules for your product and market.

Silicon dioxide suppliers

Manufacturers and distributors whose own websites say they sell it.

We are checking silicon dioxide suppliers now

Every listing is checked against the supplier’s own website before it goes live, so this list fills in over the coming weeks. The specs and COA checklist above are ready today.

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Frequently asked questions

What forms of silicon dioxide can brands buy?

Common forms include fumed (colloidal) silica, precipitated silica, hydrated silica and natural source silica. Ask each supplier for the specification sheet of the exact grade they quote.

What should the COA for silicon dioxide include?

Expect assay, loss on drying and loss on ignition, specific surface area, pH and soluble salts, heavy metals and particle size and tapped density, each with its method, specification and result for that lot.

How should silicon dioxide be stored?

Keep in sealed bags or containers in a dry place; silica readily adsorbs moisture and odors from the air, which reduces its capacity as a flow agent. The powder is extremely light and dusty, so open and dispense it with dust extraction. Shelf life or retest dates come from the supplier, often several years, with loss on drying retested.

What is the regulatory status of silicon dioxide?

21 CFR 172.480 permits silicon dioxide as an anticaking agent in food in an amount not to exceed 2 percent by weight of the food. 7 CFR 205.605 lists silicon dioxide among the synthetic substances allowed in organic products, permitted as a defoamer and allowed for other uses when organic rice hulls are not commercially available. Health Canada's List of Permitted Anticaking Agents allows silicon dioxide as an anticaking agent in listed foods, including foods sold in tablet form.

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