The Hidden Plastic Age – External Thermal Insulation Composite System In their course description from fall 2020 Studio Anne Holtrop at ETH Zürich states that “the first plastic age in architec-ture ended with the oil crisis in 1973.” From the 1950s on, synthetic plastic significantly influenced the field of architecture. The versatility, lightweight, and malleability of plastics opened new possibilities for architects.1 I argue that – at least in Germany – the plastic age in architecture did not end with the 1973 oil crisis but became a hidden building standard.