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Silica gel is graded by pore diameter, and the grade code follows from it: Type A is narrow pore, Type B is medium pore and Type C is coarse pore. Narrow pore gel adsorbs best at low humidity; coarse pore gel adsorbs best at high humidity; Type B sits between the two. Separately, "colour-changing" (indicating) grades are a different axis again — they describe what the gel does visually, and they exist on top of the pore grading, not instead of it.
Because the pore structure differs, adsorption behaviour differs too. These are the grades we supply as bulk silica gel, with the structure data published on each product page:
| Grade | Pore size | Pore volume | Surface area |
|---|---|---|---|
| Type A — narrow pore | 20–40 Å | 0.35–0.50 ml/g | ≥ 600 m²/g |
| Type B — medium pore | 50–80 Å | 0.50–0.80 ml/g | 450–600 m²/g |
| Type C — coarse pore | 80–100 Å | 0.78–1.00 ml/g | 300–500 m²/g |
The general shape of the behaviour — narrow pore wins at low humidity, coarse pore wins at high humidity — is the same principle we explain in our overview of what silica gel is.
An indicating, or colour-changing, gel is built on a narrow pore base and carries an indicator so that saturation is visible. That is a second decision, made after you have chosen the pore grade:
| Indicating grade | Colour change | Note |
|---|---|---|
| Blue indicating gel | Blue → light blue → pink | Narrow pore base; the classic, cobalt-chloride-based indicator. |
| Cobalt-free indicating gel | Orange → colourless, or orange → green | No cobalt chloride; the compliant replacement for blue in the EU and US. |
Both change colour as they take up moisture and both can be regenerated, but they are not interchangeable on compliance grounds. The reason is that cobalt chloride — the indicator in blue gel — was classified by the European Union as a Class II carcinogen in 1998, since when blue indicating silica gel has been banned or phased out in Europe and the United States. The cobalt-free grade was developed to meet that market, using a new non-toxic compound dye so there is no cobalt to declare.
This is the mix-up worth avoiding. Type A / B / C describes the pore structure and applies to plain, non-indicating gel. Blue and cobalt-free describe the indicator and are built on a narrow pore (Type A style) base. So a cobalt-free orange gel is narrow pore and indicating, while a plain white Type B bead is medium pore and not indicating. When you order, give both facts: the pore grade you need, and whether you need colour indication.
Give us the pore grade (or the duty, and let us match it), whether you need colour indication and whether cobalt-free is required, the particle form and size, the sachet or bulk packing, and the destination market if the goods are food-contact or EU-facing. Grades are quoted on request, and custom sachet weights and printed sachets are available.
Tell us the application and the market — we will point you at the right pore grade and indicator type, and quote it.
