You need a kiln or furnace lined right - the first time. Mullite insulating brick is one of the most versatile choices for backup insulation and selected hot-face positions in industrial kilns, heat-treatment furnaces, and ceramic tunnel kilns. The Al₂O₃ content ranges from 37% (JM23) to 77% (JM32), so there's a grade for almost every temperature profile between 1260°C and 1760°C.
This guide covers the full picture: technical specifications by grade, factory pricing, MOQ, ordering steps, and a practical installation checklist. If you already know which grade you need, skip straight to the How to Order section.
What Is Mullite Insulating Brick?
Mullite insulating brick is a refractory product manufactured with mullite (3Al₂O₃·2SiO₂) as the primary crystalline phase. It contains 37–77% Al₂O₃ depending on grade. The manufacturing process uses high-purity alumina, mullite aggregate, and organic pore-forming agents fired at temperatures above 1400°C.
The result: a lightweight, low-conductivity brick that holds its shape under sustained high temperatures - without the dead weight of dense firebrick.
Where does it fit in a lining system? Mullite insulating brick is typically used as:
Backup insulation behind a denser working lining
Shell-side insulation to reduce outer furnace temperature
Hot-face lining in lower-load applications (tunnel kilns, shuttle kilns, heat-treatment furnaces) where thermal cycling is frequent and abrasion is minimal
It is not the right choice for direct contact with molten metal, aggressive slag, or heavy mechanical abrasion. For those positions, look at dense high-alumina brick or refractory castable.
JM Grade Specifications - Full Comparison Table
Five standard grades cover the full industrial temperature range. Here's the data buyers actually need:
| Grade | Al₂O₃ (%) | Classification Temp (°C) | Bulk Density (g/cm³) | CCS (MPa) | Thermal Conductivity @ 400°C (W/m·K) | Thermal Conductivity @ 1000°C (W/m·K) |
|---|---|---|---|---|---|---|
| JM23 | 37 | 1260 | 0.55–0.62 | 1.2 | 0.14 | 0.20 |
| JM26 | 54 | 1430 | 0.78–0.80 | 1.6 | 0.27 | 0.33 |
| JM28 | 64 | 1540 | 0.88 | 2.1 | 0.32 | 0.38 |
| JM30 | 72 | 1650 | 1.03 | 2.5 | 0.41 | 0.45 |
| JM32 | 77 | 1760 | 1.25 | 3.5 | 0.49 | 0.53 |
Source: ASTM C155 classification standard; values from in-house production testing.
Standard size: 230 × 114 × 65mm (straight brick). Wedge, arch, and custom shapes available on request with drawing submission.
Reheating linear change (PLC): all grades hold ≤ −0.5% to −0.9% under 8-hour soak at rated temperature, confirming dimensional stability in continuous operation.
Key Features & Benefits
Low thermal conductivity → lower energy bills. JM23 at 0.14 W/m·K means your furnace shell stays cool and your fuel cost per cycle drops. We've seen ceramic kiln operators cut fuel consumption by 18–22% after switching from dense firebrick backup to JM26 insulation layer.
Lightweight construction → faster installation. At 0.55–0.62 g/cm³, JM23 bricks weigh roughly 1.0 kg per standard piece. Dense high-alumina brick at the same size: 3.2 kg. That difference adds up fast across a full kiln lining.
High thermal shock resistance → fewer emergency shutdowns. The mullite crystal structure tolerates repeated heating/cooling cycles better than most dense refractories. This matters in batch furnaces and shuttle kilns where daily cycling is the norm.
Al₂O₃–SiO₂ chemical stability → broad atmosphere compatibility. Good resistance to acid and alkali erosion. Suitable for oxidizing, reducing, and neutral atmospheres across most industrial applications.
Wide grade range → one supplier, multiple lining zones. From JM23 backup insulation at 1260°C to JM32 hot-face at 1760°C - we stock them all. One source, one shipment, one set of import documents.
Industry Applications
Ceramic & Pottery Kilns
Tunnel kilns, shuttle kilns, and roller kilns use JM26 or JM28 as the main lining with a JM23 backup layer. The thermal cycling in shuttle kilns - sometimes 4–6 cycles per day - demands a brick with solid thermal shock resistance. That's where mullite outperforms standard light-weight fire clay brick (LWFC).
Heat-Treatment & Industrial Furnaces
Annealing furnaces, hardening furnaces, and tempering furnaces in the metallurgy and automotive industries typically run 800–1200°C. JM26 handles this range with room to spare. The low heat storage (a direct function of low bulk density) means faster heat-up time - important for cycle-time-sensitive operations.
Glass Melting Furnaces
The regenerative chambers and upper structure in glass furnaces operate at 1300–1600°C. JM28 and JM30 are standard choices here. A glass plant in Egypt replaced their existing insulation layer with our JM28 bricks in 2024 - their previous solution lasted 14 months. Current installation has crossed 20 months with no reported dimensional failure.
Petrochemical Cracking & Reforming Furnaces
Cracking furnaces and steam reformers need insulation that handles thermal gradients and hydrogen atmospheres. JM26 and JM28 are widely used in these applications. Key requirement: low Fe₂O₃ content (our JM28 runs 0.8% max) to prevent catalytic reactions in hydrogen-rich environments.
Blast Furnace Stoves & Cement Kilns
Hot blast stove tops and cement preheater towers use JM28–JM30 grades in selected positions. For cement rotary kiln main barrel lining, we recommend pairing with a dense high-alumina working layer rather than using mullite insulating brick as the sole hot-face material.
How to Select the Right JM Grade
Three questions narrow it down fast:
1. What is your maximum operating temperature? Add a 50–80°C safety margin above your peak process temperature. If your furnace peaks at 1380°C, JM26 (rated 1430°C) is the minimum. Consider JM28 if thermal spikes are possible.
2. Is this a hot-face or backup position? Hot-face positions require higher cold crushing strength (CCS) and better surface stability. JM28 (CCS 2.1 MPa) or above for hot-face. JM23 or JM26 for pure backup insulation behind a denser working layer.
3. How frequent is thermal cycling? Daily cycling (shuttle kilns, batch furnaces): prioritize thermal shock resistance - JM series handles this well across all grades. Continuous operation (tunnel kilns, rotary kilns): dimensional stability (PLC) is the critical variable - confirm the rated soak test data.
One honest note: if your operating temperature stays below 1000°C and the position is purely backup insulation, calcium silicate board (CSB) will insulate better per dollar. We sell CSB too. No point overselling you on mullite if CSB fits the job.
How to Order: Pricing, MOQ & Lead Time
Factory Pricing (2025 Reference)
| Grade | Price per Piece (USD) | Price per Metric Ton (USD) | Notes |
|---|---|---|---|
| JM23 | 1.20–1.80 | 450–580 | Most common, best stock availability |
| JM26 | 1.60–2.20 | 560–680 | High-volume grade, good lead time |
| JM28 | 2.00–2.80 | 680–790 | Moderate stock |
| JM30 | 2.50–3.20 | 750–850 | Made-to-order for large quantities |
| JM32 | 3.00–4.00 | 900–1,100 | Specialized grade, confirm availability |
FOB Qingdao. Prices vary with order volume, specifications, and raw material market at time of order.
MOQ
Standard grades (JM23, JM26): 2 metric tons (approximately 1,000–1,500 pcs standard size)
JM28, JM30: 3 metric tons
JM32 and custom shapes: 5 metric tons or per project confirmation
Sample orders (testing/approval): 50–100 pcs, freight buyer's account
Lead Time
Standard grades in stock: 7–12 days ex-factory
Made-to-order standard sizes: 15–20 days
Custom shapes (wedge, arch, special cuts): 20–30 days after drawing confirmation
Payment & Shipping
Payment: T/T 30% deposit, 70% before shipment. L/C at sight for orders above USD 30,000.
Incoterms: FOB Qingdao (default), CIF available on request
Packaging: wooden pallets, waterproof wrapping; export-standard packing for sea freight
Port of loading: Qingdao. Transit to Dubai: ~18 days. To Houston: ~28 days. To Ho Chi Minh City: ~8 days.
To get a quotation, send us: grade required, quantity (metric tons or pieces), standard or custom size, destination port, and any required certifications. We reply within 4 business hours.
Installation Guide
Proper installation matters as much as product quality. Here's what our field experience shows:
Pre-Installation Checks
Before laying the first brick:
Verify brick dimensions against your lining design drawing - tolerances are ±1.5mm for standard grades.
Check for visible cracks or chips from transit; damaged bricks reduce thermal performance and structural integrity.
Confirm the mortar or adhesive is compatible with mullite insulating brick - use lightweight mullite mortar (same Al₂O₃ class as the brick) for joints.
Laying Procedure
Joint thickness: Keep mortar joints at 2–3mm. Thick joints are weak points under thermal cycling.
Bonding pattern: Use running bond (staggered joints) for wall and roof lining. Avoid cross-joints that run continuously through the lining - they create thermal bridges and structural weak lines.
Dry fit first: For arch and curved sections, dry-fit without mortar, mark the pieces, then apply mortar in the final installation pass.
Anchors: In roof applications above 1400°C, anchor bricks with refractory steel anchors (Grade 310S or ceramic anchors above 1200°C). Spacing: 200–250mm staggered grid.
Dry-Out Firing Schedule
New mullite brick linings must be dried out slowly to remove moisture and prevent cracking:
| Stage | Temperature Range | Heating Rate | Hold Time |
|---|---|---|---|
| Stage 1 | Ambient → 150°C | 20°C/hr | 4 hrs |
| Stage 2 | 150°C → 350°C | 20°C/hr | 4 hrs |
| Stage 3 | 350°C → 600°C | 30°C/hr | 2 hrs |
| Stage 4 | 600°C → Operating Temp | 50°C/hr | Per process |
Do not rush Stage 1 and Stage 2. Steam pressure from residual moisture is the most common cause of early spalling in new linings. We've had clients skip the slow ramp and call us about cracked bricks 48 hours after startup. Don't be that project.
Common Installation Mistakes
Using dense firebrick mortar on insulating brick (wrong density match, poor bonding)
Over-tightening joints above 3mm (thermal expansion has nowhere to go)
Installing in wet or freezing conditions without proper protection
Skipping the dry-out curve on replacement panels (partial replacements still need gradual heat-up)
Quality & Certifications
Every production batch at our factory goes through:
Chemical composition analysis (XRF): confirms Al₂O₃ content within ±2% of grade spec
Bulk density check: 100% sampling per pallet
Cold Crushing Strength (CCS) test per ASTM C133
Reheating Linear Change (PLC) test per ASTM C210
Our ISO 9001:2015 certification covers the full production and QC process. Certificate available on request with every order.
We keep production records for 3 years. If there's ever a quality dispute, we can trace back to the specific batch, firing date, and QC result. That's not marketing - that's a real paper trail that protects your procurement decision.
Frequently Asked Questions
What is the difference between JM23, JM26, and JM28 mullite insulating bricks?
JM23, JM26, and JM28 differ in Al₂O₃ content, classification temperature, and density. JM23 has 37% Al₂O₃ and is rated to 1260°C with a bulk density of 0.55–0.62 g/cm³ - the lightest and most insulating grade, best for backup positions. JM26 has 54% Al₂O₃ rated to 1430°C. JM28 has 64% Al₂O₃ rated to 1540°C with higher mechanical strength (CCS 2.1 MPa), making it suitable for selected hot-face positions in ceramic and industrial kilns.
What is the minimum order quantity for mullite insulating bricks?
Standard grades (JM23 and JM26) have a minimum order quantity of 2 metric tons, which is approximately 1,000–1,500 pieces in standard 230×114×65mm size. For JM28 and JM30, the MOQ is 3 metric tons. Sample orders of 50–100 pieces are available for testing and approval at buyer's freight cost. FOB Qingdao.
How long does it take to receive mullite insulating bricks from China?
For standard grades held in stock, ex-factory lead time is 7–12 days. Sea transit to the Middle East (Dubai) is approximately 18 days, Southeast Asia (Ho Chi Minh City) about 8 days, and North America (Houston) roughly 28 days. Custom shapes or non-stock grades require 15–30 days production time before shipping.
Can mullite insulating brick be used as the hot-face lining?
Yes, in certain applications. JM28, JM30, and JM32 grades are used as hot-face linings in ceramic kilns, heat-treatment furnaces, and industrial heating equipment where abrasion and molten material contact are minimal. For direct exposure to molten metal, slag, or severe mechanical impact, dense high-alumina brick or refractory castable is the better choice.
