Technical performance of the glass block

1. Introduction to the Technical Performance of Glass Blocks

The glass block is a unique architectural element: it combines transparency, strength, insulation, and durability in a modular building component suitable for both interior and exterior applications.
Unlike monolithic glass, the glass block contains an internal air chamber that enhances thermal and acoustic performance, while its solid glass mass ensures stability, safety, and controlled light
transmission.

The technical performance of a glass block depends on several factors:

• type of glass (clear, wave, satin, colored)
• surface texture
• thickness
• internal geometry
• installation system
• exposure conditions

This guide compiles and summarizes the essential performance characteristics for designers, contractors, and architectural studios, using clear, rigorous language perfectly aligned with Future Glass Block standards.

The performance areas covered include:

• light transmission
• thermal insulation
• acoustic insulation
• fire resistance
• mechanical resistance
• thermal shock behavior
• long-term durability
• façade performance

The goal is to provide a complete, reliable, and professional overview, useful both during design and product selection.

2. Light Transmission

Glass blocks allow natural light to enter interior spaces while maintaining privacy, visual comfort, and solar gain control. Optical performance depends on:

• type of glass
• surface texture
• color
• thickness
• internal geometry

The values shown are indicative and based on tests performed according to international standards (ASHRAE / EN 410), on European (~80 mm) and American (~100 mm) glass block formats.

2.1 Indicative Optical Performance

Clear Glass Blocks (transparent)
Visible Light Transmission (VLT): ~ 72–78%
Luminous Reflectance (Out/In): ~ 8.8–9.2%
Solar Energy Transmittance: ~ 66–73%
Solar Absorption: ~ 18–25%
Shading Coefficient: ~ 0.86–0.91
SHGC: ~ 0.75–0.79
U-Value (Summer): ~ 3.10–2.90 W/m²K

Maximum brightness, more direct light, ideal for spaces requiring transparency and deep daylight penetration.

Wave Glass Blocks (wavy texture)
VLT: ~ 73–75%
Solar Transmittance: ~ 68–71%
Shading Coefficient: ~ 0.87–0.89
SHGC: ~ 0.76–0.77
U-Value (Summer): ~ 3.20–2.90 W/m²K

Diffuse light, increased privacy, reduced glare.

Satin / Mist / Sandblasted Glass Blocks
VLT Satin/Mist: ~ 70–72%
VLT Sandblasted (1 side): ~ 62–64%
Solar Transmittance: ~ 60–66%
Shading Coefficient: ~ 0.82–0.86
SHGC: ~ 0.72–0.75

Maximum light diffusion, high privacy, soft and uniform atmosphere.

Colored Glass Blocks (indicative values based on Turquoise)
VLT: ~ 60–63%
Luminous Reflectance: ~ 8.7–9.0%
Solar Transmittance: ~ 54–56%
Solar Absorption: ~ 35–37%
Shading Coefficient: ~ 0.78–0.79
SHGC: ~ 0.68–0.69
U-Value (Summer): ~ 3.10–2.90 W/m²K

Softer light, warm atmosphere, strong solar gain control.

Table – Indicative Optical Performance of Glass Blocks

Elegant, generic, defensible table. No identifying references. No codes. No brands.

2.2 Factors Influencing Light Transmission

Surface Texture

• Clear: direct light, maximum brightness
• Wave: diffused light, natural privacy
• Mist/Satin: full diffusion, visual comfort
• Sandblasted: strong diffusion, ideal for bathrooms and
  private areas

Glass Color

• Colored blocks reduce VLT compared to clear blocks
• Typical values: 60–65%, depending on color intensity

Thickness

• Greater thickness slightly reduces VLT and improves thermal insulation
• Measured difference: ~ -3% between 80 mm and 100 mm

Internal Geometry

• The air chamber and internal curvature influence light diffusion and thermal behavior

2.3 Design Advantages of Light Transmission

• Controlled natural lighting
• Visual comfort
• Integrated privacy
• Energy efficiency
• Uniform atmosphere

3. Thermal Insulation of Glass Blocks

Thermal insulation in glass blocks depends on their internal structure: two glass walls separated by a sealed air chamber. This configuration reduces heat loss and improves comfort in both winter and summer.

With the HIGH PERFORMANCE range from Future Glass Block, glass blocks achieve thermal insulation values never before reached in the sector, as stated in the official documentation, where it is highlighted that HP blocks:

• reduce thermal dispersion through glass block walls
• currently guarantee the lowest Ug value ever achieved by a glass block

3.1 U-Value – Thermal Transmittance

The U-Value (Ug) indicates how much thermal energy passes through the glass block. The lower the value, the better the insulation.

HIGH PERFORMANCE Range (official values)

HP PLUS is the glass block with the lowest Ug value ever achieved in the industry.

3.2 Comparison with Standard Glass Blocks

Standard glass blocks (=80 mm, with air chamber) have typical Ug values:

• Clear / Wave / Satin / Colored: ~ 3.10–1.90 W/m²K

This means:
HP EASY (Ug 1.2) insulates ≈ 2,60× better
HP LIGHT (Ug 1.0) insulates ≈ 3.00× better
HP PLUS (Ug 0.8) insulates ≈ 3,90× better

3.3 SHGC – Solar Heat Gain Coefficient

SHGC indicates how much solar heat enters the interior space. In HIGH PERFORMANCE blocks, the combination of increased thickness (HP PLUS, HP EASY) and optimized air chamber reduces solar gain, improves summer comfort, and contributes to energy savings.

3.4 Shading Coefficient (SC)

SC represents the ability of the glass block to filter solar heat compared to standard glass. HIGH PERFORMANCE models, thanks to their greater depth and glass mass, provide superior solar control compared to standard blocks.

3.5 Table – General Thermal Comparison

3.6 HIGH PERFORMANCE vs Solid Monolithic Glass Block

The solid monolithic glass block (full glass, no air chamber) typically measures:

• 100×200×50 mm · glass thickness: 50 mm

Its mass is high, but thermally:

• it has no air chamber
• it provides no internal barrier to heat transfer
• it has significantly higher thermal transmittance than chambered glass blocks, especially HIGH PERFORMANCE models

Qualitative Comparison

The solid glass block is ideal for mechanical resistance and safety, but cannot compete thermally with HIGH PERFORMANCE glass blocks.

3.7 Design Advantages of Thermal Insulation

• Real reduction of thermal dispersion
• Superior winter and summer comfort
• Significant energy savings
• Suitable for continuous façades
• Performance compliant with energy efficiency regulations
• Transparent and satin solutions across all HP lines

4. Acoustic insulation

The acoustic insulation of the glass block depends on its glass mass, its internal geometry, and the material’s ability to attenuate sound vibrations. Thanks to its closed structure and double wall, the glass block offers superior acoustic performance compared to traditional monolithic solid glass.

The HIGH PERFORMANCE – Acoustic Insulation range by Future Glass Block is today one of the most advanced solutions in the sector, with certified values according to DIN EN ISO 140-2.

4.1 Certified acoustic values

The official page you are viewing confirms:
“The sound insulation index tested and evaluated according to DIN EN ISO 140-2 is Rw = 45 dB.”

This value places the HP Acoustic glass block among the most high-performing materials in the field of sound transmission.

4.2 New HP glass block – 50 dB

Future Glass Block has introduced a new high-performance acoustic glass block with a value of:

Rw = 50 dB

This is an exceptional result, allowing:

• insulation of environments with intense noise
• drastic reduction of background noise
• acoustic comfort even in critical spaces
• preservation of transparency and natural light

This value positions Future Glass Block at the top of the European market.

4.3 Recommended applications

HP Acoustic glass blocks are ideal for:

• bars and nightclubs
• conference rooms
• sports arenas
• discotheques
• industrial facilities
• environments with noisy machinery
• professional studios
• residential spaces adjacent to high-traffic areas

The official page confirms that HP Acoustic blocks are designed for very noisy environments while maintaining transparency and natural light.

4.4 Table – Indicative acoustic performance

The new 50 dB HP block creates a decisive gap in the market. No competitor offers this
combination of transparency + acoustic insulation + competitive price.

4.5 Technical comparison: HP block vs monolithic solid glass

Thanks to your technical sheet, we now have the real values:

Monolithic solid glass 100×200×50 mm (Crystal Full Brick)

• Rw = 43 dB
• Ug = 36 W/m²K
• Light transmission = 44% HP Acoustic glass block
• Rw = 45 dB (certified)
• Rw = 50 dB (new version)

Technical conclusion

• Monolithic solid glass has good mass → good acoustic insulation (43 dB).
• HP Acoustic glass block has an internal chamber + optimized glass mass → superior insulation (45–50 dB).
• The new 50 dB HP Acoustic block insulates about 7 dB more than monolithic solid glass. A huge difference in perceived comfort.

4.6 Design advantages of acoustic insulation

• Reduction of background noise
• Greater acoustic privacy
• Comfort in high-traffic environments
• Ability to maintain natural light without sacrificing silence
• Ideal solutions for commercial and industrial architecture
• Certified performance according to international standards

5. Introduction to fire resistance

Fire resistance is one of the most important performance factors in the design of glass-block walls.
When discussing fire compartmentation, it is not only about materials: it is about safety, protection, continuity of escape routes, and the integrity of the building.

The HIGH PERFORMANCE – RF line includes glass blocks designed to achieve fire resistance performance up to EI 120 minutes, as declared on the official HP Fire Resistance page.

The range includes:

• RF30 – 30-minute fire resistance
• RF60 – 60-minute fire resistance
• RF90 – 90-minute fire resistance
• RF120 – 120-minute fire resistance

5.1. Reference standards

Fire resistance tests are carried out according to:

• • EN 1364-1 – Fire resistance tests for non-load-bearing elements
• EN 1363-1 / EN 1363-2 – General requirements and additional methods
• EN 13501-2 – Fire resistance classification
• DIN EN 1051-2 – Glass blocks for construction
• DIN EN 13501-2:2010-02 – EI120 class

5.2. RF range – Fire resistance performance

5.2.1 RF30 – 30-minute fire resistance

Blocks designed to guarantee:

• Integrity (E) 30 minutes
• Insulation (I) 30 minutes
• Possible extensions up to E 60 / EW 60 depending on the tested system

5.2.2 RF60 – 60-minute fire resistance

Typical performance:

• EI 60 minutes
• Possible extensions up to E 90 / EW 90

5.2.3 RF90 – 90-minute fire resistance

Typical performance:

• E 90–100 minutes
• Radiation (W) measured up to approx. 90–100 minutes

5.2.4 RF120 – 120-minute fire resistance

The RF120 block represents the highest performance available:

• EI 120 minutes
• Compliant with DIN EN 13501-2:2010-02
• Declared as “the world’s first glass brick resistant to fire for 120 minutes” on the official HP page

5.3. Summary table of performance

5.4. Fundamental warning: what has been tested and what has NOT been tested. Fire resistance tests refer exclusively to the glass blocks.

Official test reports certify only the behaviour of the glass blocks tested under specific laboratory conditions.

No installation system has been certified.

To achieve the declared performance, the tests used:

• specific types of mortar
• specific reinforcements
• specific metal profiles
• specific insulating materials
• specific wall geometries
• specific expansion joints

But these materials and methods have NOT been certified. They were used only to perform the test, not to certify an installation system.

Real-world installation can completely change fire performance.

If an installer uses:

• unsuitable mortar
• non-compliant metal profiles
• joints not resistant to fire
• non-certified insulating materials
• different geometry
• an unexpected fire-exposure side
• an inadequate supporting structure

The declared performance cannot be guaranteed.

5.5. Technical responsibility notice (mandatory)

The performance values reported derive exclusively from official test reports carried out by accredited laboratories.

Future Glass Block:

• does not certify installation systems
• does not guarantee the fire resistance of the finished work
• cannot be responsible for installation carried out by third parties
• cannot guarantee performance if materials different from those used in the tests are employed

The final classification of the work must be verified by:

• fire-safety designer
• site management
• competent authority

The information provided is for informational purposes and does not constitute product certification.