insert is one way to slightly adjust the volume of a bottle, without building a completely new mould. A volume insert attaches to the inside of a mould, creating a circular indentation on the side of the finished bottle. Different size inserts can be used as manufacturing circumstances change, for example mould temperature or cooling rate. The volume of finished bottles is periodically measured, and volume inserts are changed as needed. Environmental comparisons Many potential factors are involved in environmental comparisons of returnable vs non-returnable systems. Researchers have often used life cycle analysis methodologies to balance the many diverse considerations. Often the comparisons show benefits and problems with all alternatives. One recent life cycle study of one-way recyclable HDPE bottles indicated the importance of secondary packaging: returnable plastic crates can allow lower tare weight bottles. Reuse of bottles requires a reverse logistics system, cleaning and, sanitizing bottles, and an effective Quality Management System. A key factor with glass milk bottles is the number of cycles of uses to be expected. Breakage, contamination, or other loss reduces the benefits of returnables. A key factor with one-way recyclables is the recycling rate: In the US, only about 30–35% of HDPE bottles are recycled. Examples See also Gallon smashing, internet challenge involving participants deliberately spilling milk in a supermarket by breaking containers Tea set, which includes a small jug for milk or cream References Books, general references Yam, K.L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, External links Milk containers Liquid containers Retail packaging