What Is Calsil (Calcium Silicate) Insulation?
Calsil is shorthand for calcium silicate insulation — rigid, asbestos-free boards and pipe sections rated to 650°C (standard) or 1000–1050°C (high-temp grade).
Calsil is the shorthand the industry uses for calcium silicate insulation — a rigid, asbestos-free board and pipe-section material rated for continuous service up to 650°C, with high-temperature grades reaching 1000–1050°C. It is the rigid, load-bearing cousin of rock wool: less flexible, but it holds its shape, carries weight, and gives a clean structural surface inside furnace and kiln casings.
What Is Calcium Silicate Insulation Made Of?
Modern calsil is produced by reacting lime and silica under high-pressure steam (autoclaving) to form crystalline calcium silicate — typically the tobermorite or xonotlite phase — reinforced with a small amount of organic or inorganic fiber for toughness. It contains no asbestos (unlike the old "asbestos millboard" it replaced) and emits no harmful fibers during normal handling.
Key Properties at a Glance
| Property | Typical value |
|---|---|
| Continuous service temp | 650°C (standard); 1000–1050°C (high-temp grade) |
| Density | 170–240 kg/m³ (boards); 200–300 kg/m³ (pipe sections) |
| Thermal conductivity | ~0.048–0.060 W/m·K at 50–100°C; ~0.10–0.12 W/m·K at 600°C |
| Compressive strength | ~0.5–1.0 MPa at 10% deformation (rigid, load-bearing) |
| Fire rating | A1 non-combustible |
| Water uptake | Low capillary absorption; dimensionally stable when wet |
| Other | Low shrinkage, chemically inert, rot/pest resistant |
The standout property is rigidity with low thermal conductivity — calsil can be walked on, bolted through, and used as a structural layer, which rock wool and ceramic fiber blankets cannot do.
Calsil vs Rock Wool vs Ceramic Fiber
| Calsil | Rock wool | Ceramic fiber | |
|---|---|---|---|
| Max service temp | 650–1050°C | ~750°C | up to 1430°C |
| Form | Rigid board/pipe | Flexible blanket/board | Flexible blanket/module |
| Compressive strength | High (load-bearing) | Low | Low |
| Handling dust | Minimal | Fibrous | Fibrous (PPE advised) |
| Cost | Mid | Low | Higher |
Rule of thumb: choose calsil where you need a rigid, dimensionally stable surface or a backup layer that won't slump; choose rock wool blanket for irregular or curved surfaces on a budget; choose ceramic fiber where temperature exceeds 1000°C.
Common Forms: Board, Pipe, Block
- Board — the most common form, used as kiln/boiler back-up lining, fire-rated wall and duct cores, and oven panels.
- Pipe sections — pre-curved segments for hot process pipes, often used in power and petrochemical plants.
- Block / custom shapes — for kiln car decks, ladle covers, and engineered furnace components.
Typical Applications
Calsil is widely specified in high-temperature industrial linings: cement kiln back-up and transition zones (see cement kiln thermal protection), power-plant boiler casings and ducts (power generation applications), petrochemical heaters, fire-rated doors and panels, and marine fire barriers. It is frequently the rigid layer in a composite lining — ceramic fiber or rock wool on the hot face, calsil as the structural backup.
How to Specify Calsil
- Temperature class — 650°C standard or 1000°C grade for hotter zones.
- Density grade — higher density = higher strength and slightly lower conductivity, at more weight and cost.
- Dimensions & facing — board thickness, pipe OD/ID, and whether a facing (foil, tissue) is needed.
- Standards — confirm A1 non-combustible certification and any plant-specific spec.
Frequently asked
What temperature can calcium silicate insulation withstand? +
Standard calsil is rated for continuous service at 650°C (1200°F). High-temperature grades are formulated for 1000–1050°C. Above that, ceramic fiber or polycrystalline mullite boards are the better choice.
Is calsil waterproof or water resistant? +
Calsil has low capillary water uptake and stays dimensionally stable if it gets wet — it does not soften or slump like some organic foams. It is water-resistant, not waterproof: prolonged immersion should be avoided, and the system should dry out.
Is calcium silicate insulation asbestos-free? +
Yes. Modern calcium silicate insulation is made from lime, silica, and reinforcing fibers under autoclave curing. It contains no asbestos and is safe to handle without the precautions required for legacy asbestos millboard.
Is "calsil" the same as calcium silicate? +
Yes. "Calsil" is simply trade shorthand for calcium silicate insulation board or pipe section. You will see the two terms used interchangeably across datasheets and specifications.
Can calsil be used for pipe insulation? +
Yes. Calsil is available as pre-formed pipe sections and curved boards for hot process piping in power, petrochemical, and steam systems — pairing low conductivity with the rigidity to stay in place without external support.