Insulation Glossary: A1, Calsil, Pyrogel, Microporous Explained

Industrial insulation specifications are full of shorthand: A1, Calsil, Pyrogel, Microporous. Each term points to a different material class, and picking the wrong one for a given temperature or fire requirement can cost energy, safety, or project budget.

This glossary explains what each term actually means, where the terms overlap, and how to choose among them.

A1 — The Non-Combustible Fire Rating

A1 is the top fire-performance class under EN 13501-1 and the equivalent grade in China's GB 8624-2025 system. An A1-rated material is non-combustible: it does not burn, does not produce flaming droplets, and has very low smoke development.

Key points:

• Organic content is typically ≤1%.
• Common A1 insulation materials include rock wool, glass wool, calcium silicate (Calsil), and ceramic fiber.
• A1 is a fire classification, not a material type. Two products with very different thermal performance can both be A1.

For any public building, hospital, school, high-rise, or enclosed process area where fire safety is regulated, A1 is usually the minimum acceptable rating.

Calsil — Rigid Calcium Silicate Insulation

Calsil is short for calcium silicate insulation — a rigid, inorganic board or pipe-section material made from lime (CaO) and silica (SiO₂) cured under high-pressure steam. The resulting crystal structure (usually tobermorite or xonotlite) gives it low thermal conductivity plus enough strength to carry light loads.

Typical grades and properties:

Use Calsil when you need a rigid, structural back-up layer — for example behind a hot-face ceramic fiber lining, under pipe support shoes, or as a flat, walkable insulation surface. For a deeper dive, see our Calsil FAQ.

Pyrogel — Aerogel-Based Blanket Insulation

Pyrogel is one of the best-known brand names for silica aerogel blanket insulation. In everyday specification language, "Pyrogel-type" has become shorthand for high-performance aerogel blankets — thin, flexible, hydrophobic, and extremely low in thermal conductivity.

Key properties:

• Thermal conductivity: ~0.017 W/m·K at 25°C; ~0.025–0.030 W/m·K at 250°C.
• Service temperature: typically −90°C to 650°C continuously; short peaks to ~1200°C.
• Density: 160–220 kg/m³.
• Hydrophobicity: water-repellent (>95% typically), which reduces corrosion-under-insulation (CUI) risk.
• Form: flexible blanket, easy to wrap around valves, flanges, and curved pipes.

The trade-off is price: aerogel blankets cost several times more than mineral wool per square metre. They pay back fastest where space is tight, access is difficult, or CUI shutdowns are expensive. For a full comparison, read our Pyrogel vs Mineral Wool Pipe Insulation guide.

Microporous — Nano-Scale Pore Insulation

Microporous insulation uses a solid matrix filled with pores smaller than the mean free path of air molecules (typically <50 nm, often in the 0.2–2 nm IUPAC micropore range). Because the pores are so small, gas molecules cannot move freely, so heat transfer by convection and gas conduction is suppressed.

Key properties:

• Thermal conductivity: 0.020–0.040 W/m·K at room temperature; ≤0.065 W/m·K at 1000°C.
• Service temperature: roughly −200°C to 1150°C, depending on the chemistry.
• Density: 220–350 kg/m³.
• Forms: rigid boards, flexible panels, pipe sections, and custom-molded shapes.
• Composition: alumina-based, silica-based, or calcium-silicate-based, often with reinforcing fibers.

Microporous sits between aerogel and Calsil on the performance/cost map: thinner than Calsil, more mechanically robust than aerogel, and rated for higher continuous temperatures than Pyrogel-type blankets.

Comparison Table

How to Choose

• Need only fire compliance on a budget → A1-rated rock wool board or glass wool.
• Need a rigid, load-bearing back-up layer behind the hot face → Calsil board or pipe section.
• Space is tight, CUI is a concern, or valves/flanges need frequent access → Pyrogel-type aerogel blanket.
• Continuous temperature is above 650°C and you need thinner sections than Calsil → microporous board or flexible microporous panels.

In practice, many high-temperature linings are hyid: ceramic fiber or rock wool on the hot face, Calsil or microporous as the structural back-up, and aerogel blankets at critical details like flanges and valves.