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Photo: Hasopor AB

Measuring Circular Economy in Construction: Hasopor's foam glass product

RISE collaborates with companies interested in measuring the circularity of their products and services. Recently, researchers at RISE collaborated with Hasopor AB to measure the circularity of their foam glass product, which is used as light weight fill material for construction projects and made almost entirely of recycled glass.

Hasopor believed they had a circular product, but how circular?

The Circular Economy is a fast-growing global movement that aims to improve both economic- and environmental wellbeing through more efficient re-use of the stuff already in circulation today. Ultimately, businesses, governments, and other enthusiasts of the Circular Economy aspire to dramatically reduce the extraction of planetary resources while eliminating the concept of “waste” entirely. Familiar approaches to improving circularity include refurbishment programs, material recycling, modular product design and other techniques that make it easy to repair and upgrade existing products rather than manufacture new products from newly extracted virgin material.

Despite enthusiasm for the Circular Economy on every continent, one common challenge remains: accurately measuring and reporting circularity. A manager leading their company through a transition toward circularity will want to answer questions like…

  • How “circular” is my product or service? How can I improve it?
  • How does the circularity of my product compare to similar products? and ideally
  • How much money do I save (or lose) per unit of circularity gained (or lost)?

It was with an interest in measuring the circularity of their product that Hasopor AB reached out to RISE. Hasopor produces foam glass  (“skumglas” in Swedish), a synthetic rock-like substance used as light-weight fill material in the foundation of buildings, roads, bridges, and rail projects. Traditional foundation fill material is made from crushed stone mined from quarries or larger rocks. While options for recycled fill material exist—for example recycled concrete or fill material recovered from former construction sites—these sources are intermittently available and typically of poorer quality  than either “virgin” stone aggregate or foam glass. Foam glass is also lighter than stone, so it can be transported relatively easily.

Most importantly, foam glass is made almost entirely of recycled ingredients: shredded household glass, glass powder, and the chemical silicon carbide (SiC). All the glass content used in Hasopor’s product comes from recycled sources. Explains one Hasopor employee, “The recycled glass we use is the quality of recycled glass that typically can’t be re-sold or re-used. No one wants it. But it is ideal for making foam glass.”  In other words, Hasopor had good reason to believe its product was “circular” because its product was made from material used before. But how circular?

Using the C-Metric to benchmark circularity

There is now a large and growing number of methods for measuring circularity. By one estimate, as of 2020 there are 70 existing firm- or product-level circularity metrics developed around the world by academics and industry. Researchers in the Sustainable Business Unit (Division Samhällsbyggnad) at RISE have positioned themselves on the forefront of this effort, having collaborated with Swedish businesses and public sector organizations to develop metrics that are both objective and practical to apply.

The C-metric

One tool, called the C-Metric has been applied by RISE researchers on products in multiple industries. The C-Metric is a ratio of the economic value of a product’s recirculated parts to the economic value of all its parts:

C= The economic value of a product's recirculated partsThe total economic value of a product

C is expressed as a number 0 through 1, where 1 represents a product whose value is composed entirely of recirculated (e.g. re-used, refurbished, recycled) material, and 0 represents a product made entirely of un-used virgin material. The metric was developed by RISE researchers as way to express the circularity of a product as a single number.  Its creators decided to use economic value to assign weight to the circularity of each component because economic value is the best-known representation of scarcity in the marketplace and serves as a proxy for societal relevance. In other words, the C-Metric is more sensitive to material that is rare or in high demand over material that is common or not highly demanded—no matter that material’s mass or volume.

   One recently published analysis suggests that products with higher (more circular) C-Metric scores have lower global warming impacts relative to “typical” marketplace alternatives. The C-Metric is also designed to be calculated without having to rely on complicated mathematical formulae or judgement calls about how long a product will last in the future.

As a simple example, my bicycle worth SEK 10.000 is made entirely of virgin material except for a re-used seat (inherited from my former bicycle) worth SEK 1.000. This bicycle would have a C-Metric score of 0,100 (1.000/10.000 = 0,100). If I decide to add SEK 500 worth of re-used lighting equipment— purchased from my neighbor who no longer needs his bicycle accessories— it would alter the score slightly. Now, the full product is worth SEK 10.500 with a combined SEK 1.500 of recirculated components. With my re-used lights, my bicycle is not only safer to ride at night, but also slightly more circular, with a C-Metric score of 0,143 (1500/15000 =  0,143).

 Of course, the more components a product has, the more complicated the calculation becomes, however the concept is rather straightforward and can be applied, in theory, to any product for which data about component costs and recirculated content can be accessed. 

Applying the C-Metric to Hasopor’s Foam Glass

Hasopor’s foam glass product consists of three ingredients: recycled household glass, glass power made from entirely from recycled glass, and the chemical silicon carbide (SiC). The first two ingredients account for a combined 98,6 percent of the mass and 99,8 percent of the volume of the finished product. SiC accounts for a relatively miniscule proportion of the mass or volume of the foam glass product. Since both glass ingredients are made entirely from recirculated content, Hasopor’s product would score a nearly perfect 1.0 C-Metric score if the C-Metric weighted the ingredients by their mass (a fairly common way to weight components in circularity metrics), or volume (a rather uncommon way to weight components in circularity metrics). However, the C-metric is weighted by each component’s economic value, and that very small amount of SiC is a relatively high-value ingredient, representing 42 percent of the total product cost per unit.

SiC is a ceramic material generated in an electric furnace by combining petroleum coke and quartz sand around a graphite core. According to Hasopor’s SiC supplier, these ingredients are all “virgin” ingredients. The ingredients are subjected to extremely high temperatures (1700-2500 degrees Celsius). After cooling, multiple qualities of SiC emerge, including a very fine powder used by Hasopor in its foam glass production. SiC’s extreme hardness makes it ideal for other applications like fine sandpapers, disk brakes, and military armor. It is also resistant to extreme heat conditions and is thus the main ingredient in mirrors mounted on satellites and space stations. While there are ongoing efforts to improve the reuse  and recycling of SiC products, there is still no economical way to generate the very fine SiC powder from recycling. It was therefore determined that the SiC ingredient in Hasopor’s product was 100% virgin, or 0% circular.

The two glass products are made entirely of recirculated content, and thus both have c-scores of 1,00. Their c-scores are multiplied by their respective proportion of economic value in one unit of foam glass product. Since SiC is a virgin product (c = 0), its contribution to the summed C-Metric score is zero. The final C-Score for the foam glass product is 0,581, meaning that 58,1 percent of the economic value of  foam glass comes from recirculated content. 

In summary, the foam glass product is 99,8% circular when measured in terms of volume, 98,6% circular when measured in terms of mass, and 58,1% circular when measured in terms of economic value. 


Understanding their product’s C-score allows Hasopor to benchmark its progress in the Circular Economy. It can also serve as a benchmark to other firms in the foam glass industry and to construction firms interested in sourcing its materials from “circular” vendors.   Without new ways to obtain SiC powder from recirculated sources or lower the value of SiC relative to other ingredients in their product, Hasopor may have reached the maximum level of circularity for foam glass. Yet the score is also important in comparison to fill material that is created from mined stone aggregate—an entirely virgin (non-circular) product—or foam panels used for insulation and support in construction foundations—a petroleum product made typically from virgin resources. Additional sustainability benefits of foam glass are discussed in detail on the Hasopor website.

The Circular Economy is more than one firm or one innovator. The goals of the Circular Economy will only be achieved once entire networks of manufacturers and suppliers collaborate to generate products and services that take advantage of material already in circulation.  Ultimately, the more firms take steps to measure, report, and improve their circularity, the easier it will be for other manufacturers, suppliers, and clients to “go circular.”


Project name

Circular Economy and foam glass




Region Örebro län

RISE role in project


Project start


3 månader


Hasopor AB, Hasopor AB

Supports the UN sustainability goals

9. Industry, innovation and infrastructure
12. Responsible consumption and production
Robert Boyer

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Robert Boyer

Senior Researcher

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