Glass — Flat / Sheet

Material Composition Assumptions

The default reference product is 1 kg of clear soda-lime float glass (4-6 mm thick), the standard architectural and automotive glass:

• Silica sand (SiO2): ~72% of batch weight. High-purity industrial silica sand.
• Soda ash (Na2CO3): ~13% of batch. Lowers the melting point from ~1700 degC to ~1500 degC. Produces process CO2 when decomposing in the furnace.
• Limestone (CaCO3) and dolomite: ~12% combined. Stabilizers that improve durability. Also produce process CO2 from calcination.
• Minor additives: Alumina, iron oxide, sulfate fining agents, ~3% combined.
• Cullet (recycled glass): Typically 15-30% of batch for float glass (lower than container glass due to quality requirements).

The float glass process (molten glass floated on a tin bath) produces optically flat sheet glass. Melting temperature of ~1550-1600 degC in a regenerative gas-fired furnace is the dominant energy input. Process CO2 from carbonate decomposition adds approximately 0.2 kgCO2/kg glass beyond fuel combustion emissions.

Manufacturing Geography

Float glass production is concentrated among a few global producers:

• China: ~50% of global flat glass production. Major producers include CSG Holding and Fuyao Glass.
• EU: Saint-Gobain (France), AGC (Belgium), NSG/Pilkington (UK), Guardian.
• USA: Guardian, Vitro, NSG/Pilkington.
• Japan: AGC, NSG.
• Grid intensity (China): 565 gCO2e/kWh (IEA 2024).
• Rationale: Float glass production is a thermal-dominated process (>85% of energy is natural gas for melting). Scope 1 emissions from gas combustion and carbonate decomposition dominate. Grid electricity is a minor contributor.

Regional Variation

Production Region	Fuel Source	Estimated Score (per kg)	Adjustment vs Default
Global average (default)	Natural gas	1.0 kgCO2e	Baseline
EU (best practice)	Natural gas + high cullet	0.7-0.8 kgCO2e	-25%
China	Natural gas or coal-gas	1.1-1.3 kgCO2e	+15%
USA	Natural gas	0.9-1.0 kgCO2e	-5%
Electric melting (future)	Renewable electricity	0.3-0.5 kgCO2e	-60%

Note: Unlike most products, grid intensity has minimal effect on flat glass because the process is dominated by direct fuel combustion (Scope 1). The fuel type and cullet fraction are the primary levers.

Provenance Override Guidance

A supplier may override the default CCI score by submitting:

1. Environmental Product Declaration (EPD) per EN 15804 or ISO 14025 for the specific float glass product.
2. Cullet fraction data: Higher cullet input reduces melting energy by ~2.5% per 10% cullet increase and eliminates carbonate process emissions for the recycled fraction.
3. Furnace efficiency data: Modern regenerative furnaces are more efficient than older recuperative designs.
4. Coating data: Low-E coated glass, toughened glass, and laminated glass have additional processing steps that increase production emissions by 10-30%.

Methodology Notes

• CCI score of 1 kgCO2e/kg represents a global average for uncoated float glass, consistent with industry EPD data (0.7-1.2 kgCO2e/kg) and Glass for Europe LCA data.
• Scope breakdown: Scope 1 dominates at 60% (0.6 kgCO2e/kg) from natural gas combustion and carbonate process CO2 — making flat glass one of the most Scope 1-dominated products. Scope 3 is 30% (0.3 kgCO2e/kg) from raw material extraction and transport. Scope 2 is 10% (0.1 kgCO2e/kg) from annealing and cutting electricity.
• Confidence: High — extensive EPD data and industry LCA from multiple global producers.
• Functional unit: 1 kg of clear float glass (4-6 mm), cradle to gate.
• Processed glass: Low-E coated glass adds ~0.2-0.3 kgCO2e/kg. Toughened (tempered) glass adds ~0.1-0.2 kgCO2e/kg. Laminated safety glass adds ~0.3-0.5 kgCO2e/kg for the PVB interlayer.