Recycled materials are applied regularly in building industry, especially materials that no more have aesthetic or hygienic qualities for use elsewhere. Recycled plastics are quite young and hardly researched for application in buildings. Most studies were made on the implementation of cut plastics or plastic fibres into concrete or asphalt. We developed an innovative application of recycled PET in architecture in the form of a building block, which is produced by the blow-moulding technology: a standard technology of producing packaging of beverages. Based on our previous research on the use of PET bottles in architecture, we developed a new interlocking shape of a bottle, which can be used to build structures. This so-called PET(b)rick can be interlocked perpendicularly and also in parallel which allows the construction of walls in traditional way. The load-bearing medium is air, but the cavity of the brick also allows for filling with different materials. The first test of load-bearing capabilities of such a structure was an exhibit at EXPO 2015 in Milano, where we assembled a bench made out of 72 PET(b)ricks. This object can carry more than 120 kilograms and is used as seat as well as illumination and decoration of the space.