Glass is one of the few materials that can be recycled indefinitely without loss of quality, yet recycling rates vary enormously between countries. The differences owe less to technology than to logistics and habit: collection systems that separate glass by colour produce far purer cullet, which manufacturers can substitute directly for raw sand, soda ash and limestone. Every tonne of cullet used saves roughly 1.2 tonnes of raw material and cuts furnace energy use, because cullet melts at a lower temperature than its raw ingredients. Countries with deposit-return schemes consistently report the highest collection rates, suggesting that a small financial incentive changes behaviour more reliably than public appeals.