Nanochannel glass replica membranes, a recent invention, can be used for parallel patterning of substrates, for example as a shadow mask in reactive ion etching. The preparation of the membranes—formed by physical vapor deposition on wafers that have been cut from bundles of two types of glass fibers that are repeatedly drawn down to the correct dimensions—their uses and their advantages are described. How the size, position, geometric pattern, and packing density of the voids in the membranes can be controlled to a high degree is outlined.