Honeycomb has been described as a product, a concept, a technique, and a material, while it is actually some of each. Whichever description fits best, honeycomb is most familiar to engineers as a structural material in sandwich form, mostly for aircraft application.In the last few years, honeycomb has fulfilled other needs besides structural ones and has been used to solve design problems in products other than aircraft.Advances in many directions highlight the success of lightweight cores.The future developments and use may hinge on materials and methods.