A SPIDER's silk has as much strength as steel fibre of the same size and can stretch and rebound from at least 10 times its original length, giving the silk properties superior to metal or synthetic fibre. The only problem is that it is not practical to harvest silk from spiders for commercial use because they produce such small quantities. It would take about 400 spiders working full-time just to get enough silk for one square yard of cloth. Cornell University researchers have been studying spider silk structure with an eye to duplicating the fibre materials in genetically-engineered plants. So far they have defined the crystalline structure of spider silk fibres, and they are working to understand how the liquid material is processed as it travels through a duct within the spider's body. 'During the journey through the duct, silk molecules align themselves, becoming organised and partially crystalline,' said Alexandra Simmons, one of the Cornell researchers who reported on their progress to a meeting of the American Chemical Society.