Highland manufactures insulating fire brick (IFB) in four ASTM C155 grades: K23 (bulk density 0.60 g/cm³, working temp 1100°C), K26 (0.80 g/cm³, 1350°C), K28 (0.90 g/cm³, 1450°C), and K30 (1.00 g/cm³, 1550°C). Al₂O₃ content 38–75% across grades.
Thermal conductivity 0.22–0.42 W/m·K at 600°C. Fe₂O₃ <1.0% — suitable for reducing atmosphere service in petrochemical and hydrogen furnaces. Dimensional tolerance ±0.5mm after six-side grinding.
ISO 9001:2015 certified with batch density and conductivity test reports. Standard grades ship within 35–65 working days. Submit your furnace type and operating temperature for grade recommendation.
Highland manufactures insulating fire brick (IFB) in four ASTM C155 grades: K23 (bulk density 0.60 g/cm³, working temp 1100°C), K26 (0.80 g/cm³, 1350°C), K28 (0.90 g/cm³, 1450°C), and K30 (1.00 g/cm³, 1550°C). Al2O3 content 38–75% across grades. Thermal conductivity 0.22–0.42 W/m·K at 600°C. Fe2O3 <1.0% — suitable for reducing atmosphere service in petrochemical and hydrogen furnaces. Dimensional tolerance ±0.5mm after six-side grinding. ISO 9001:2015 certified with batch density and conductivity test reports. Standard grades ship within 30–40 working days. Submit your furnace type and operating temperature for grade recommendation.
K23–K30
ASTM C155 Grades
0.22–0.42
W/m·K at 600°C
±0.5mm
6-Side Grinding Tolerance
35–60
Working Days Lead Time
Request Grade Datasheet & Pricing →
| Property | K23 | K26 | K28 | K30 |
|---|---|---|---|---|
| Classification Temp (°C) | 1260 | 1430 | 1540 | 1650 |
| Working Temp (°C) | 1100 | 1350 | 1450 | 1550 |
| Bulk Density (g/cm³) | 0.60 | 0.80 | 0.90 | 1.00 |
| CCS (MPa) | ≥ 1.2 | ≥ 2.0 | ≥ 2.5 | ≥ 3.0 |
| Thermal Cond. at 600°C (W/m·K) | 0.22 | 0.28 | 0.35 | 0.42 |
| Al2O3 (%) | 38–42 | 42–46 | 50–60 | 65–75 |
| Fe2O3 (%) | < 1.0 | < 1.0 | < 0.8 | < 0.7 |
| Standard Dimensions (mm) | 230×114×65 / 230×114×75 — Custom sizes available | |||
Insulating Fire Brick, also known as Lightweight Refractory Brick or Soft Brick, is a type of refractory material specifically designed for its insulating properties. Unlike dense firebricks (hard bricks), which are intended for structural strength and resistance to mechanical wear, IFBs are characterized by high porosity, low bulk density, and exceptional thermal resistance.
At Highland Refractory, we utilize a specialized burn-out manufacturing process. We mix high-purity refractory clays with organic fillers (such as sawdust or polymer beads). During high-temperature firing, these organic materials burn away, leaving behind a uniform network of microscopic air pockets. These trapped air pockets act as a barrier against heat transfer, resulting in one of the lowest thermal conductivity values in the refractory industry.
The K23 brick offers the lowest density and highest insulation value in the K-series. Primary application: backup insulation behind dense refractories or hot-face linings in low-velocity, clean-firing environments.
K26 provides a balance between mechanical strength and thermal resistance. Primary application: hot-face linings for ceramic shuttle kilns, heat treatment furnaces, and forging furnaces where direct flame contact is required.
Designed for high-temperature stability where K26 would suffer from excessive shrinkage. Primary application: petrochemical heaters, ammonia reformers, and carbon bake furnaces.
Premium high alumina specialty brick for ultra-high-temperature scenarios. Primary application: hydrogen furnaces, glass tank crowns, and advanced laboratory kilns.
Iron Oxide (Fe2O3) is the enemy of refractory stability. In reducing atmospheres where CO or Hydrogen is present, iron acts as a catalyst for carbon deposition, causing bricks to disintegrate. Highland IFBs feature ultra-low iron content (typically <0.8%), making them ideal for petrochemical cracking and hydrogen furnace applications.
Heat leaks most often occur at the joints. Every Highland brick undergoes automated six-side grinding after firing. Our dimensional tolerance of ±0.5mm ensures that masonry joints are as thin as possible, creating a virtually airtight seal that further reduces energy loss.
Our proprietary slurry matrix allows bricks to withstand rapid temperature fluctuations. This is essential for batch kilns and furnaces that undergo frequent startup and shutdown cycles.
Iron & Steel: In blast furnace stoves and annealing furnaces, IFBs are used as secondary insulation. By reducing the temperature of the outer steel casing, they prevent shell deformation and improve the safety of the working environment.
Petrochemical & Chemical Processing: Our K26 and K28 grades are the preferred choice for lining ethylene crackers and primary reformers, where they provide long-term stability under high pressure with low-iron chemical purity.
Ceramics & Glass: Using lightweight K23/K26 bricks for kiln cars and walls allows for faster firing cycles, directly increasing production capacity and lowering the cost per unit of ceramic ware.
Aluminum & Non-Ferrous: Highland IFBs are used in carbon bake furnaces and aluminum melting furnaces as backup insulation, providing a stable thermal gradient that protects dense refractory bricks.
Weight: IFBs are 60% to 75% lighter than dense bricks. This reduces the structural load on the furnace steelwork, allowing for lighter and cheaper furnace designs.
Heat Storage: Dense bricks act as heat sinks, soaking up massive amounts of energy. IFBs have low heat storage, meaning the heat stays inside the furnace.
Thermal Conductivity: IFBs offer a 300% to 500% improvement in insulation value compared to dense firebricks.
Cutting and Shaping: IFB is easy to work with — you can use standard woodworking handsaws, drill bits, and routers. Always wear a P2/N95 respirator mask and safety goggles when cutting.
Mortar Selection: IFBs must be laid with a compatible insulating refractory mortar. We recommend an air-setting mortar that matches the temperature grade of the brick (e.g., K26 Mortar for K26 Bricks).
Expansion Joints: Leave expansion gaps every 1.5 to 2 meters, filled with ceramic fiber blanket or expansion strips, to absorb thermal movement.
Thin-profile requirements: IFB is available in standard thicknesses of 65mm (2.5 inch) and 75mm (3 inch). For applications requiring reduced-thickness insulating fire brick — split bricks, soap bricks, or precision-ground profiles down to 25mm — custom grinding is available on request. For standard thin-profile refractory brick sizes and specifications, see our dedicated Thin Refractory Brick product page
Thermal Spalling: Caused by heating the furnace too fast. Moisture trapped in the pores turns to steam and cracks the brick. Solution: Follow a strict bake-out schedule.
CO Disintegration: Caused by high iron content in the brick reacting with CO gas. Solution: Use Highland's Low-Iron (Fe2O3 < 1.0%) series.
Mechanical Abrasion: Soft bricks are not meant for areas with falling debris or heavy metal impacts. Solution: Use a "hard face" of dense bricks in impact zones with IFB behind them.
Bricks are stacked on reinforced wooden pallets with cardboard corner protectors. Each layer is separated by cardboard, and the entire pallet is heavy-duty shrink-wrapped. We ship LCL for small repairs or FCL for major furnace builds.
K23 (1100°C service, 0.60 g/cm³) is for backup insulation behind dense refractories only — never contact flame directly. K26 (1350°C service, 0.80 g/cm³) is for hot-face linings in ceramic kilns and heat-treatment furnaces. Rule of thumb: use K23 behind a hard face to maximize heat savings; upgrade to K26 when the lining surface exceeds 1100°C.
Yes. Grades K26, K28, and K30 are designed for direct flame and heating element exposure. K23 is for backup only. Because IFBs are soft (CCS 1.2–3.0 MPa), do not use them in zones with heavy mechanical impact or abrasion — use a "hard face" of dense fire bricks in impact zones with IFB behind them.
Specify Al2O3 ≥65% (K28/K30) and Fe2O3 <0.7%. In reducing atmospheres containing CO or H2, higher iron content catalyzes carbon deposition, causing the bricks to disintegrate. Low-iron K28/K30 bricks prevent this chemical failure.
Choose IFB if the lining must bear structural weight, operates continuously above 1200°C, or faces high-velocity gas erosion. Choose ceramic fiber if you need rapid heat-up/cool-down cycles or lightweight backup insulation below 1200°C. Best practice: use an IFB hot face with a ceramic fiber blanket backup.
MOQ: 1 metric ton per grade for standard sizes (230×114×65/75mm). Mixed shipment: yes, you can mix different grades on separate pallets in one container. Custom shapes — grooved or arch bricks — have a 0.5-ton MOQ and 40–60 working days lead time from drawing confirmation. Standard grades ship in 30–40 working days.
