jersey, in the channel islands, was famous for its knitting trade in medieval times, and because of that original fame, the name jersey is still applied to many forms of knitted fabric, round or flat. the traditional jersey, and traditional guernsey, are dyed a navy blue colour, using a dye that does not require stripping the wool of its natural oil, rendering these sweaters surprisingly water resistant. the wool used in guernseys is often passed through oil in order to render it doubly water-resistant.