Dear Jiaxuan: Do you know when you ‘laminate’ a piece of paper in order for it to be durable and waterproof? it is like encasing the piece of paper in plastic on each side, and then the clear plastic edges stick to each other. The plastic is clear so you can still read the page.   That is similar to how our sails are made. They are ‘layered’, with the strength filaments (kevlar primarily) running from corner to corner along the ‘load paths’. Load paths are how the sail is stressed when it is set, so the strength fibres are laid along these paths that a computer simulation has predicted. There is a mylar substrate which starts the construction, the load fibres are sandwiched in between the mylar and a thin sheet of Dacron cloth, which doesn’t really add any strength, but does add some toughness for the sail for abrasion. This whole layering process is then glued together, and compressed,. Then you have your sail!

Question submitted by Jiaxuan Yan, Shanghai Datong High School, China