How to choose between glass wool products A1 and A2?

I. Definition of combustion grade and grading logic

According to the national standard GB 8624-2012 ‘Combustion Performance Grade of Building Materials and Products’, the combustion grade is a scientific quantification of the combustion characteristics of building materials in a fire. The core grading basis includes three items:

1. Heat value release (PCS): the total heat released by combustion per unit mass of material;

2. Flame spreading speed: the speed of the flame spreading on the surface of the material during combustion;

3. Smoke toxicity and droplets: the toxicity of the smoke produced by combustion and whether it produces molten droplets.

The standard classifies the combustion level into:

Class A (non-combustible materials): A1 (highest level), A2 (second highest level);

Class B (combustible materials): B1 (refractory), B2 (combustible), B3 (flammable).

The essential difference between Class A and Class B: Class A materials do not participate in combustion in a fire, only as a ‘heat bearer’; while Class B materials will release heat, fuelling the fire, becoming a ‘combustion participant’.

II. Common heat preservation and thermal insulation material combustion level comparison

Material Type	Typical Products	Common Combustion Grade	Calorific Value (PCS) Range
Inorganic Material	Glass Wool, Rock Wool, Foamed Cement	A1 or A2	≤2.0~3.0 MJ/kg
Modified Organic Material	Flame-Retardant Polystyrene Board (EPS/XPS)	B1	3.0~8.0 MJ/kg
Common Organic Material	Common Polyurethane (PU), Polystyrene Board	B2	8.0~25.0 MJ/kg
Flammable Material	Polystyrene Foam (Non-Flame Retardant)	B3	>25.0 MJ/kg

Note: Glass wool is mainly composed of molten glass fiber, which is an inorganic material and naturally non-flammable. It is one of the current mainstream A-level thermal insulation materials.

III. The glass wool ‘Class A non-combustible’ property analysis

Glass wool is classified as a Class A material due to its physical and chemical non-combustible properties:

Composition stability: The main component is silicon dioxide (SiO₂), with a melting point of over 800°C, and cannot be ignited at ordinary fire temperatures (400–600°C);

No heat release contribution: no flame spread, no dripping, and low smoke toxicity (CO≤1000ppm) in the combustion test.

But please note: Class A glass wool ≠ all products are Class A1! Its grade needs to be further distinguished based on product form, coating, and density.

IV. Which glass wool products are Class A1? Which are Class A2?

1. Core conditions for Class A1 glass wool

a. Heat value requirements: PCS ≤ 2.0 MJ/kg for homogeneous materials;

b. Additional tests: Must pass the non-combustibility test (GB/T 5464):

c. Temperature rise in the furnace, ΔT ≤ 30°C

d. Mass loss rate ≤ 50%

e. Continuous burning time = 0.

Typical A1-level products:

High-density uncoated glass wool board (ρ≥48kg/m³)

Glass wool felt made of high-quality binder (such as Sichuan Zaisheng acrylic resin base, bio-based resin base)

2. Technical threshold of A2-level glass wool

Relaxed calorific value: homogeneous material PCS ≤ 3.0 MJ/kg;

Optional test path:

Pass the non-flammability test (ΔT≤50℃, Δm≤50%, tf≤20s)

Or

Pass the monomer combustion test (FIGRA≤250W/s, THR≤7.5MJ).

Typical A2-level products:

Glass wool board for ventilation ducts with aluminum foil coating (FFR)

Medium-density glass wool strips (ρ≥32kg/m³)

Key comparison: The core difference between A1 and A2-level glass wool

Parameter	Class A1	Class A2
Calorific Value (PCS) Upper Limit	≤2.0 MJ/kg	≤3.0 MJ/kg
Non-combustibility Temperature Rise (ΔT)	≤30°C	≤50°C
Continuous Burning Time (tf)	0 s	≤20 s
FIGRA (Fire Growth Rate Index)	No requirement	≤250 W/s
Cost	High (Stricter process)	Medium

V. Engineering selection logic: When to use A1? When to use A2?

Scenarios where A1 is mandatory (according to GB 50016-2014 "Code for Fire Protection Design of Buildings"):

1. External wall insulation system of super high-rise buildings (>100m);

2. Crowded places: external walls and evacuation passages of hospitals, schools, and shopping malls;

3. Special facilities:

    a. Elderly care facilities (independent or area>500m²)  

    b. Insulation in refuge floors and fire stairwells;

4. Cavity-free adhesive curtain wall: when there is no cavity between the insulation layer and the wall and no fire isolation zone.

Scenarios where A2 is allowed:

1. Ordinary residential external walls (27m＜height≤100m), which can be used in combination with fire isolation zones;

2. External insulation of ventilation ducts (additional aluminum foil coating is required);

3. Fireproof coating of steel structures (non-load-bearing parts);

4. Metal-faced sandwich panel filling layer.

Note on design conflicts: If glass wool is compounded with other materials (such as glass fiber felt), the overall combustion level is determined by the weakest component! For example: when glass wool (PCS=1.8) is compounded with black glass fiber felt (PCS=6.9), the overall calorific value exceeds the standard and cannot pass the A2 certification.

VI. Summary: The necessity of choosing Grade A glass wool

1. Compulsory regulations: The national standard clearly requires that Grade A materials must be used in crowded places and super high-rise buildings;

2. Reasons for fire dynamics: Grade A materials do not participate in combustion and can block the "three-dimensional fire spread.";

3. Toxicity control: Reduce the release of deadly toxic gases such as CO and HCN.

Ultimate advice:

1. Under the premise of controllable costs, A1 grade glass wool is preferred - it not only meets the current specifications, but also reserves safety redundancy for future building fire protection standard upgrades.

2. Under the premise of multiple requirements (acoustic noise reduction, processing protection, non-ultra-high temperature, low fire hazard), A2 grade glass wool with various surface layers and edge sealing operations is preferred - it not only meets the actual use of acoustics, thermal insulation, and manual processing requirements, but also does not need to excessively pursue fire protection.

If you have purchase needs for high-quality rock wool and glass wool or want to learn more about the products, please contact our EcoFox insulation team.