cullet

Cullet is broken or waste glass that is suitable for remelting in glass furnaces. It includes post-consumer cullet recovered from the waste stream, such as bottles and jars, and manufacturing or internal cullet generated during the production and handling of glass products. As a key feedstock for glassmaking, cullet can lower energy use, reduce raw material requirements, and divert waste from landfills.

Processing of cullet involves collection, sorting by color (such as clear, green, and brown), and cleaning to remove contaminants like labels, metal closures, paper, plastics, and other non-glass materials. The cullet is then crushed to a controlled particle size and may be washed. Color sorting is important to maintain the desired color and quality in the final product.

Usage and limitations: In many furnaces, cullet replaces a portion of the batch ingredients (sand, soda ash, limestone) and can constitute a substantial share of the feedstock. Common formulations allow a wide range of cullet content, depending on color, furnace design, and quality controls. Contamination by non-glass materials or impurities can cause defects, reduce mechanical properties, or introduce unwanted color.

Environmental and economic aspects: Using cullet reduces energy consumption during melting, lowers fuel costs, and decreases emissions associated with raw material extraction and processing. It also decreases waste disposal needs and can support circular economy goals. However, cullet quality, contamination levels, and collection logistics affect its value and the economics of recycling programs.

Cullet is most widely used in container glass manufacturing, where it helps to produce bottles and jars efficiently, though it is also employed in other glass products and processes.