Glass can theoretically be infinitely recycled.
In order to harvest this potential, Glass for Europe’s members strive to implement circularity into their processes, where feasible. Significant efforts have been performed by EU flat glass manufacturers in order to improve glass cullet collection and recovery.
Introducing glass cullet in the furnace brings significant advantages: it reduces the use of virgin raw materials, it lowers the energy consumption needs, and it decreases greenhouse gas emissions.
Recycled content of flat glass is therefore a crucial notion for reducing carbon emissions strategies. As such, it requires an unambiguous definition, outlining its elements and its calculation methodology. The purpose of the present position paper is to provide such a harmonised definition for the European flat glass sector.
RECYCLED CONTENT DEFINITION
In standards
According to section 7.8.1.1 of the standard EN ISO 14021:2016 Environmental labels and declarations:
Recycled content is defined as proportion, by mass, of recycled material in a product or packaging.
Only pre-consumer and post-consumer materials contribute to recycled content.
Pre-consumer material is defined as material diverted from the waste stream during a manufacturing process. Reutilisation of materials such as rework, regrind or scrap generated in a process and capable of being reclaimed within the same process that generated it is excluded from pre-consumer material.
Post-consumer material is defined as material generated by households or commercial, industrial and institutional facilities in their role as end-users of the product which can no longer be used for its intended purpose.
Applied to flat glass sector (see also Annex I)
- Furnace process cullet
Furnace process cullet refers to cullet generated by a glass melting furnace for quality rejects or other reasons (i.e., edge trims, geometrical losses, etc.) during a production period or during a non-production period (i.e. crushing, colour transition, furnace draining), through any furnace exit (forming exit, furnace drain-out during production or at furnace emptying), capable of being re-introduced in a glass melting furnace on the same or another manufacturing site with no other treatment than crushing and/or standard magnetic/metallic separation.
It is suitable for re-introduction in a glass melting furnace on the same or another manufacturing site.
Furnace process cullet covers material rejected and taken out at the float line stage, as well as potential cullet transferred from line 1 to line 2 on the same site. All such rejects are however remelted to ensure material efficiency and avoid waste.
For better clarity, in the rest of the document, the denomination ‘furnace line rejects’ is used when considering the cullet output of the furnace production line, and ‘furnace process cullet’ when these rejects are re-introduced in the melting process.
As furnace process cullet is reintroduced in the process that generated it, this cullet is excluded from pre-consumer material as defined in EN ISO 14021:2016.
- Pre-consumer cullet
In the flat glass sector, pre-consumer cullet is any cullet which results from industrial operations starting with stacking of glass after its exit from the glass melting furnace and ending at the stage where the product achieves finished-product status. This includes cut-offs, losses during coating, laminating, bending and other processing steps, including the manufacture of insulating glass units or automotive windscreens. This cullet may or may not need beneficiation before being recycled into a glass furnace. Cullet collected from glass processing line on the same manufacturing site as the glass melting furnace is pre-consumer cullet. Cullet collected from third-party glass processing companies is also considered pre-consumer cullet.
Pre-consumer cullet is considered as pre-consumer material as defined in EN ISO 14021:2016 and is taken into account in recycled content.
- Post-consumer cullet
Post-consumer cullet refers to cullet originated from finished products before, during or after their use at the consumer market.
It includes returns or breakages of finished products from the transport and distribution chain as well as all material coming from glass recycling collection schemes such as glass from construction and demolition waste or from end-of-life vehicles, etc.
Post-consumer cullet is considered as post-consumer material as defined in EN ISO 14021:2016 and is taken into account in recycled content.
- Other recovered materials used in the flat glass sector
In addition to cullet, other recovered materials can be used in the flat glass sector in substitution of virgin raw materials. Because these other recovered materials may have a content which may be lost during combustion in the furnace, their contribution in the recycled content calculation shall be taken into account considering their loss on ignition (generally referred as LOI, here lign).
Loss on ignition measures the ratio of mass loss that a material undergoes when it is heated to a high temperature to initial mass. This mass loss can be attributed to the release of volatile substances such as water, carbon dioxide, organic material and other gases. This ratio is a figure between 0 and 1.
CALCULATION METHODOLOGY
Recycled content in flat glass products must be calculated according to following formula: 
where:
Detailed explanation:
According to ISO 14021, the recycled content is defined as the mass of recycled material in a product. For float glass, we consider this to be the mass of recycled material in the packed glass divided by the mass of packed glass.
The mass of packed glass produced during the basic glass production is determined by the yield of the melting furnace process. It corresponds to the difference between the mass of the melted glass and the mass of furnace line rejects. From a manufacturing point of view, the objective is to reduce as much as possible the furnace line rejects generated and to reintroduce them directly as furnace process cullet. Usually, mass of furnace process cullet is equal to mass of furnace line rejects.
Beside this usual situation, one should pay special attention to the two specific situations where the mass of furnace process cullet reintroduced in the furnace is bigger or smaller than the mass of the line rejects.
In practice, it is not always feasible to reintroduce cullet from furnace line rejects instantly: some incidents or specific practices on the furnace production line can lead to variations of rejects production or rejects reintroduction over time. Then, for a given type of product and a given period, the furnace line rejects generated and reintroduced as furnace process cullet during the manufacturing of this product are not always balanced. This leads to 3 different cases: the mass of furnace process cullet can be equal, superior or inferior to the mass of furnace line rejects (refer to the visuals below).
- -If mfpc = mlr: The whole quantity of cullet from the melting process is neutral in the balance of input and output flows. The recycled content, which corresponds to the mass of recycled material in the packed glass divided by the mass of packed glass, is calculated as follows:
- If mfpc > mlr: A ‘surplus’ of furnace process cullet is used as input, in addition to the amount of furnace line rejects that turns in loop. This ‘surplus’ of furnace process cullet is coming from the manufacturing of another type of product produced in the plant, is coming from another furnace or was generated during a previous time period. Nevertheless, as this ‘surplus’ has been generated by a melting furnace, it must not be considered as recovered material when reintroduced in this process. This surplus contributes to the mass of packed glass and should therefore not decrease the mass of glass on which the recycled content is calculated. Thus, the recycled content is calculated as follows:
- If mfpc < mlr: Some furnace line rejects cannot be reintroduced as furnace process cullet (e.g.quality does not allow for use in the furnace). In such case, the recovered material is split over the packed glass and the line rejects lost as waste or by-products (fraction of the line rejects which is not reintroduced in the furnace as furnace process cullet). As there is no preferential allocation of the recovered material in the packed glass, the recycled content is calculated over a volume equal to the sum of packed glass plus the lost line rejects, that is to say the melted glass minus the line rejects reintroduced in the furnace as furnace process cullet.
One shall also note that the formula considers cullet as made of glass only. It may happen that the cullet source includes minor organic materials that will be lost during the melting process. This is usually what happens when recycling laminated glass: in the formula, one shall use the mass of glass only, and not include the mass of interlayer, otherwise, the LOI of this material would have to be applied.
Note: While striving to keep the best possible record of the various flows, if companies are unable to segregate the mass of furnace production cullet from the mass of pre- and post-consumer cullet entering the melting furnace, manufacturers can use best available knowledge and engineering estimates to determine the mass of each type of cullet.
Post-consumer recycled content:
It is possible to consider only post-consumer recycled content by using the same calculation, by considering only post-consumer materials.
PROCESSED GLASS PRODUCTS
EN ISO 14021:2016 applied to processed glass products like laminated glass or insulated glass units results in the recycled content being calculated by making the sum of each part’s recycled content multiplied by its mass fraction:
- Laminated glass: the recycled content is the sum of the mass fraction of glass multiplied by the recycled content of glass and the mass fraction of interlayer multiplied by the recycled content of the interlayer.
- Insulated glass unit: the recycled content is the sum of the mass fraction of glass multiplied by the recycled content of glass and the mass fraction of each of the other components multiplied by its recycled content (spacer bar, sealant, etc.).
Where i refers to the different components (glass, PVB, spacer bar, sealant, etc.) and 𝑚𝑖 and 𝑅𝑐 𝑖 are respectively the mass and the recycled content of component i.
Annex I: Limits between different cullet types within the boundaries of flat glass production process (FprEN 17074:2026 (E))
Annex II: Relevant legislation and standards
On waste:
(1) DIRECTIVE 2008/98/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 19 November 2008 on waste and repealing certain Directives (“WFD”): concepts and definitions related to waste management, including the definitions of waste, recycling, and by-product
(2) COMMISSION REGULATION (EU) No 1179/2012 of 10 December 2012 establishing criteria determining when glass cullet ceases to be waste under Directive 2008/98/EC of the European Parliament and of the Council.
On Product Category Rules (PCR for EPD):
(3) EN 15804:2012+A2:2019/AC:2021 Sustainability of construction works – Environmental product declarations – Core rules for the product category of construction products
(4) prEN 17074:2025 Sustainability of construction works – Environmental product declarations – Product Category Rules for flat glass and channel shaped glass products
(5) PCR for Glass products used in automotive and transport industry: 2023, written by Saint-Gobain
On recycled content:
(6) EN 45557:2020 – General method for assessing the proportion of recycled material content in energy-related products
On Product labelling:
(7) EN ISO 14021:2016 Environmental labels and declarations – Self-declared environmental claims (Type II environmental labelling)
(8) EN ISO 14025:2010 (WI=CSS26023) – Environmental labels and declarations – Type III environmental declarations – Principles and procedures
