Clear Lessons For Recycling Glass In Building Products

James Vallette | September 30, 2015 | Materials

Glass Cullet Report Cover
The use of recycling materials in building products is evolving. The latest version of the Leadership in Energy and Environmental Design (LEED version 4) green building rating system no longer explicitly credits recycled materials, but it does reward transparency and disclosure of product lifecycles and contents. While recycling is more important than ever because of the need to make use of dwindling world resources, recycling's supply chain is murky and far from transparent. As Wes Sullens and Barry Hooper note in an upcoming Healthy Building Network newsletter, "This truly is the age of transparency for building products. Yet in this new light, recycled content can find itself somewhat in the dark." [1]

Economics aren't helping either. The rise of single-stream recycling contaminates waste streams and devalues recycled feedstocks, while at the same time prices for virgin materials have dropped due to fracking and low energy prices. And US export markets are more demanding than ever, requiring higher quality (cleaner) feedstocks at more competitive prices. 

Our new Healthy Building Network report on the use of recycled glass in building materials shows how we can reverse these trends - and create high-quality recycled content for building products made in the USA. Post-Consumer Cullet in California is the second in our Optimizing Recycling series of recycled feedstock evaluations. It reveals how best practices by regulatory bodies, recycled feedstock processors, and manufacturers can improve feedstock value, protect human health, and dramatically increase recycling rates.

Source separation of waste streams and toxic content restrictions create a multitude of economic and environmental benefits. The value of cullet increases. The wasteful landfilling of discarded glass (nationally, only 28% is recycled) decreases. Manufacturers need less energy to produce insulation, leading to lower greenhouse gas emissions. And workers, surrounding neighborhoods, and the environment at large are exposed to fewer toxic contaminants. 

There is a direct correlation between the purity of glass cullet and the ability of fiber glass insulation manufacturers to incorporate this recycled material into their products. Heavy metals - particularly lead - pose technical challenges in the fiber glass manufacturing processes.

In North America, the insulation industry has adopted an ASTM standard that restricts proportions of heavy metals in cullet to 0.1% (1,000 parts per million [ppm]). [2] It can do much better. In Europe, these same manufacturers restrict heavy metals to just 20 ppm - fifty times lower.

As a result, fiber glass insulation made in Europe typically contains much more recycled glass. Insulation made in Belgium and the United Kingdom contains about 80 percent cullet - about twice the average recycled content found in US fiber glass insulation. This means big savings in energy costs. According to the US Environmental Protection Agency, "for every 10 percent of recycled content in fiber glass insulation, the manufacturing energy needs decrease by roughly 3.25 percent." [3] It also means far fewer heavy metals are processed in these factories and released to the environment.

In California, cullet used in building products does not achieve the European limits on heavy metal content, but it is far cleaner than the 1000 ppm heavy metal content allowed by the ASTM standard. The recycled glass used to make fiber glass insulation is reliably low in toxic metals because the sole supplier of recycled glass to the state's insulation factories produces cullet in compliance with the California's Toxics in Packaging law. This law restricts the heavy metal content of four heavy metals (lead, cadmium, mercury, and hexavalent chromium) to 100 ppm, or ten times lower than the ASTM standard. [4] Quality controls designed for bottle producers have the incidental side benefit of providing insulation cullet that is compliant with packaging regulations. Therefore, we have determined that cullet as used in fiber glass insulation made in California does not raise significant human health or environmental concerns.

Elsewhere in the United States, where industry standards are not yet protective of human health, the heavy metal content of cullet supplied to insulation factories varies considerably. [5]

The California and European experiences with cullet are lessons in optimization. These lessons can be applied beyond cullet, to the vast array of potential recycled feedstocks that may be used in building products. In this virtuous cycle, human and environmental health are protected, manufacturers pay less for feedstocks and energy, and resources are reused, not landfilled, burned, or extracted from the earth. Our Optimizing Recycling Collaboration series seeks to uncover these stories and provide recommendations for improving feedstock quality and greater recycling rates.


[1] Wes Sullens is Green Building Program Manager for StopWaste, a public agency responsible for reducing the waste stream in Alameda County, CA. Barry Hooper is a Green Building Specialist for the City and County of San Francisco's Department of the Environment (SFE). StopWaste, SFE, and the Healthy Building Network have developed a new framework for evaluating the hazards, supply chains, and economic impacts of recycled feedstock streams found in building products. Our collaboration soon will release an overview report, Optimizing Recycling: Criteria for Comparing and Improving Recycled Feedstocks in Building Products.

[2] ASTM International, Standard Specification for Glass Cullet Recovered from Waste for Use in Manufacture of Glass Fiber, Reapproved 2010.  

[3] WARM: Fiberglass Insulation. US Environmental Protection Agency.  

[4] Other state regulations and incentives also help. The California Beverage Container Recycling and Litter Reduction Act - in which consumers pay a deposit on beverages sold in recyclable bottles and cans, and return them for redemption - helps to keep bottles separated from the waste stream. Source separation prevent cross-contamination from problematic glass types, like compact fluorescent bulbs and cathode ray tubes, which contain mercury and lead, respectively. In addition, the California Department of Conservation's Quality Incentive Payment (QIP) Program, which pays curbside programs, drop-off or collection programs, and other certified entities to sort and clean material to QIP specifications.

[5] The country's second largest cullet processor did not respond to our requests for information and has been named a serious repeat offender of environmental and occupational health laws for lead contamination. Insulation factories in Ohio and Texas supplied by this processor report disproportionate amounts of lead releases, compared to other fiberglass manufacturers.

CORRECTION: An earlier version of this newsletter contained an error in a footnote, which stated that the “second largest cullet processor… recently filed for bankruptcy…”.   A glass company with a similar name filed for bankruptcy, but is a separate entity. HBN regrets the error.