When a specification calls for a "Thermiculite® filled gasket", two questions follow: is this a material or a brand, and will an equivalent be accepted?
What vermiculite is
Vermiculite is a natural mineral, a layered aluminium-iron-magnesium silicate close to the mica group. Heated, the water between its layers evaporates and the mineral expands. That expanded structure gives a stable, non combustible material at high temperature.
Its key property for sealing is this: unlike graphite, it does not lose mass through oxidation. Graphite burns away over time in oxidising service above roughly 450 °C, so the gasket thins and loses load. Vermiculite does not behave that way.
What Thermiculite® is
Thermiculite® is the registered trademark Flexitallic uses for its vermiculite based sealing materials. The base material is vermiculite; the brand identifies that company's process and product family.
In practice the distinction means:
| Term | What it is |
|---|---|
| Vermiculite | The natural mineral, the generic material name |
| Vermiculite tape / paper | The processed form used as gasket filler |
| Thermiculite® | Flexitallic's registered product family |
| "Thermiculite® equivalent" | A vermiculite based filler suited to the same service |
When a specification names a brand
Three routes exist:
1. Supply the branded product. Price and lead time follow the brand owner's programme. 2. Obtain substitution approval. A vermiculite based gasket is submitted with documentation that it meets the temperature and service conditions. 3. Update the specification. On new projects it is healthier to write performance criteria than a brand: filler material, temperature limit, oxidation behaviour and test scope.
See what is an approved manufacturer list for how approval processes run.
Where it comes up
Lines running hot in oxidising atmospheres: flue gas and exhaust ducts, catalytic units, furnace surroundings, the hot sections of steam lines and joints with fire safety requirements.
Share your service temperature and fluid data and we will compare graphite, vermiculite and mica options: enquiry form.
FAQ
Is Thermiculite® a material name?
No, it is a Flexitallic trademark. The base material is the mineral vermiculite.
Does vermiculite replace graphite?
It is more stable at high temperature and in oxidising service. It is not needed everywhere; graphite suffices on most process lines.
Are equivalent fillers accepted?
It depends on the specification, but substitution approval with documented performance is usually possible.
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