A zip includes: a pair of stringer tapes, each of which supports a row of teeth; the teeth on the two tapes being mutually opposing and capable of interdigitation thereby to fasten one stringer tape to another; a slider, adapted to move along and whose motion is guided by the rows of teeth, the slider being adapted to cause interdigitation of the teeth as a result of motion along the teeth in a first direction, and to disconnect the teeth by motion along the teeth in a second direction; wherein the first and second stringer tapes are formed of a matrix of threads interspersed with a waterproof material.