Graphite Polystyrene or Mineral Wool? Comparing Insulation Materials
Choosing an insulation material is one of the first and most important decisions in building thermal modernization. The two most popular solutions — graphite polystyrene and facade mineral wool — differ not only in price but also in physical properties, durability, and applications. In this article, we provide a detailed comparison of both materials to help you make an informed decision.
Basic Parameters — Numerical Comparison
| Parameter | Graphite Polystyrene EPS 032 | Facade Mineral Wool |
|---|---|---|
| Lambda coefficient | 0.031-0.033 W/(m·K) | 0.034-0.041 W/(m·K) |
| Density | 14-20 kg/m³ | 80-160 kg/m³ |
| Fire reaction class | E (easily flammable) | A1 (non-combustible) |
| Vapor permeability (mu) | 20-40 | 1-2 |
| Water absorption | 2-5% by volume | up to 1% (hydrophobized) |
| Price (15 cm) | 55-75 PLN/m² | 70-110 PLN/m² |
| Durability | 40-60 years | 50-80 years |
| Weight (15 cm) | 2.1-3.0 kg/m² | 12-24 kg/m² |
Thermal Conductivity Coefficient (Lambda)
The lambda coefficient is the key insulation parameter. The lower it is, the better the material insulates.
Graphite Polystyrene
Thanks to the addition of graphite, which reflects infrared radiation within the material’s structure, graphite polystyrene achieves lambda = 0.031-0.033 W/(m·K). This is approximately 15-20% better than classic white polystyrene (lambda = 0.038-0.042).
In practice, this means that 14 cm of graphite polystyrene provides the same insulation as 18 cm of white polystyrene — a real saving in thickness and cost.
Mineral Wool
Facade wool achieves lambda = 0.034-0.041 W/(m·K), depending on density and manufacturer. The best lamellar products approach graphite polystyrene in parameters, but average facade wool has a lambda of 0.036-0.038.
Verdict: Graphite polystyrene wins in thermal insulation performance — at the same thickness, it provides better protection against heat loss.
Fire Safety
This is one of the most important aspects where the materials differ dramatically.
Graphite Polystyrene — Class E
Polystyrene is a flammable material. Although it contains self-extinguishing additives (it does not sustain flame after removing the fire source), in fire conditions:
- It melts and flows, creating burning droplets
- It releases toxic gases (carbon monoxide, hydrogen cyanide)
- Ignition temperature is approximately 350-370°C
For this reason, building regulations require the use of mineral wool fire barrier strips around window openings and at each floor level in buildings above 12 m.
Mineral Wool — Class A1
Mineral wool is a completely non-combustible material:
- Withstands temperatures up to 1,000°C without losing its structure
- Does not release toxic gases
- Acts as a natural fire barrier
Verdict: Mineral wool is decidedly safer in terms of fire protection. In multi-family buildings, public utility buildings, and wherever fire safety is a priority, wool is the only appropriate choice.
Vapor Permeability
Vapor permeability (expressed by the diffusion resistance factor mu) affects the wall assembly’s ability to remove moisture.
Graphite Polystyrene (mu = 20-40)
Polystyrene is a material with relatively high diffusion resistance. Water vapor passes through it slowly, which can lead to:
- Moisture condensation at the boundary between insulation and wall
- Mold and fungi problems with poor execution
- The need for effective room ventilation
Mineral Wool (mu = 1-2)
Wool is a highly vapor-permeable material — it offers practically no resistance to diffusing water vapor. As a result:
- The wall “breathes” naturally
- Condensation risk is minimal
- Ideal for walls made of highly vapor-permeable materials (aerated concrete, perforated ceramics)
Verdict: Mineral wool wins decisively. For houses made of brick, perforated ceramics, and aerated concrete, vapor-permeable wool ensures an optimal indoor microclimate.
Sound Insulation
Graphite Polystyrene
Due to its low density and rigid structure, graphite polystyrene practically does not improve the acoustic insulation of walls. In some cases, it can even worsen acoustic parameters (membrane resonance effect).
Mineral Wool
Thanks to its fibrous, springy structure and high density, mineral wool is an excellent sound-absorbing material. A 15 cm layer of facade wool improves the acoustic insulation of a wall by 5-8 dB, which is a clearly perceptible difference.
Verdict: If the house is located on a busy street, near railway tracks, or an airport, mineral wool is a much better choice.
Durability and Dimensional Stability
Graphite Polystyrene
- Maintains insulating properties for 40-60 years
- Not resistant to UV radiation — requires immediate protection after installation
- Can be damaged by solvents and chemicals
- Susceptible to mechanical damage (birds, insects)
Mineral Wool
- Maintains parameters for 50-80 years
- Does not degrade under UV exposure
- Chemically and biologically resistant
- Less susceptible to damage by rodents
Verdict: Mineral wool is more durable, but the difference under typical usage conditions is not dramatic.
Price Comparison
For insulating 200 m² of facade with a 15 cm layer (material + labor):
| Item | Graphite Polystyrene | Mineral Wool |
|---|---|---|
| Insulation material | 11,000-15,000 PLN | 14,000-22,000 PLN |
| Adhesive and mortar | 4,000-5,500 PLN | 4,500-6,000 PLN |
| Mechanical anchors | 1,500-2,500 PLN | 2,000-3,500 PLN |
| Labor | 14,000-20,000 PLN | 16,000-24,000 PLN |
| Total | 30,500-43,000 PLN | 36,500-55,500 PLN |
The price difference averages 20-30% in favor of graphite polystyrene.
Debunking Popular Myths
Myth 1: “Polystyrene rots after 20 years”
False. Properly installed and render-protected polystyrene maintains its properties for decades. Problems arise with poor execution (thermal bridges, leaks).
Myth 2: “Wool absorbs water and loses insulation value”
Partially true, but… Modern facade wool is hydrophobized — it repels water. Absorption is minimal, and after drying, wool regains full insulating properties. The key is proper detail execution and prompt render protection.
Myth 3: “Graphite polystyrene is dark, so it overheats”
True, but with a caveat. The dark color causes graphite polystyrene to heat up more in the sun than white polystyrene. Therefore, after bonding, it should not be exposed to sunlight for more than 2-3 weeks. This is an organizational requirement, not a flaw of the material itself.
Myth 4: “Wool is always better”
False. Wool has advantages in vapor permeability, acoustics, and fire safety. But graphite polystyrene wins in thermal insulation per centimeter of thickness and is less expensive. The choice should depend on the specific situation.
When to Choose Graphite Polystyrene?
- Single-family house, single or two-story (up to 12 m height)
- Walls made of materials with low vapor permeability (reinforced concrete, silicate blocks)
- Limited budget
- Need for minimal insulation thickness (e.g., near property boundaries)
- Building with good mechanical ventilation
When to Choose Mineral Wool?
- Multi-family and public utility buildings (fire safety regulations requirement)
- Walls made of vapor-permeable materials (aerated concrete, perforated ceramics)
- Buildings exposed to noise (near roads, railways, airports)
- Timber and timber-frame structures
- When fire safety is the priority
- Buildings without mechanical ventilation
Summary
There is no single universally superior material. Both graphite polystyrene and mineral wool are proven, certified solutions that have been used successfully for decades. The key is matching the material to the building type, wall construction, and the investor’s needs.
At Elewacje z Klasą, we help clients select the optimal insulation material based on a technical analysis of the building. We carry out insulation work with both graphite polystyrene and mineral wool, always with full documentation and warranty.
Not sure which material to choose? Schedule a free consultation with our technical advisor. We operate in the Kraków and Małopolska area.