This flexible and reusable building prototype originally came out as our reaction to the unique Chinese phenomenon in recent decades’ building frenzy -- the production of vast amount of flamboyant but short-lived showroom buildings for the sales of real estate developments. Yet it is a building system that can be easily adapted to many different functions, and most importantly disassembled after each use and reassembled in another location, thus preventing huge waste of resources. It is part of our continued efforts in exploring the ultimate potential of building sustainability - reusable buildings. Enabling speedy construction, it is a building system that is light, industrialized, flexible, sustainable and reusable. The prototype V1.0 was realized in Beijing China in 2013, and the prototype V2.0 named HEX-SYS was completed in Guangzhou China recently in 2015. This prototype was inspired by the ancient Chinese wooden building system which can be taken apart and rebuilt elsewhere with almost no damage. The prototype V1.0 looks like a horizontal silver tube floating above water, recalling 60s’ experimental space capsules. Devised from one modular system, the steel structural skeleton, and the composite floor panels made from steel and concrete, are prefabricated and bolted together on site. Both the solid aluminum panels and the glass panels take on the same module, which allows a somewhat free arrangement of openings on the façade according to different program requirement behind. Internally, the space is organized with one bridge that connects 5 boxes that each contains different types of functions. The interior décor can vary, as well as the positions of the five boxes.