Fibreglass begins as sand and ends as filaments thinner than a human hair, drawn from molten glass at speeds that rival a car on the motorway. The batch is a carefully balanced oxide recipe. E-glass, the workhorse of the composites industry, is roughly: - 52 to 56 percent silica (SiO2), the network former - 12 to 16 percent alumina (Al2O3) for chemical durability - 16 to 25 percent calcia (CaO) to lower melt viscosity - 5 to 10 percent boron oxide (B2O3) as a flux and electrical insulator Silica sand, limestone, kaolin clay and colemanite are fed into a gas-fired furnace operating near 1,400 to 1,550 °C, where they fuse into a homogeneous, bubble-free melt. The critical step is fiberisation. Molten glass flows into a bushing, an electrically heated tray of platinum-rhodium alloy perforated with hundreds to several thousand precision nozzles. Platinum is chosen because almost nothing else survives prolonged contact with molten glass without contaminating it. Each nozzle releases a d...