The estimate was calculated by correlating the respective weights and densities of the recyclable and non-recyclable materials of a vehicle. In particular:

Physical properties of ASR, or "fluff": density - range, 300 to 400 kg/m³; moisture content - range, 1 to 20 percent, with an average of 8 percent. Assuming 350 kg/m³ and 8 percent moisture, ASR has a density of 322 kg/m³ on a dry-weight basis. [Source: Correspondence with Dr. Michael Day, National Research Council Canada, Institute for Chemical Process and Environmental Technology, Polymeric Materials, February 1999]

Physical properties of recyclable materials, primarily metals: assume a density of 3200 kg/m³ (considering void space between fist-sized chunks and the possible range of metal densities: aluminum, 2,673 kg/m³; iron and steel (which is the vast majority of metal material utilized in current vehicles), 7160 to 7889 kg/m³; copper, 8907 kg/m³). [Source: Perry's Chemical Engineers' Handbook, Sixth Edition, McGraw-Hill, 1984]

An average vehicle (1,400 kg) contains 1050 kg of metal - aluminum, iron and steel, copper, zinc, etc. - and 350 kg of non-recyclable materials - plastics, rubber, glass, etc. (i.e., 75% recyclables/25% ASR, by weight).