Metallic substrates for catalysts constitute a supporting technology to meet the various emission legislations world wide for passenger cars as well as for 2- and 3-wheelers.Hot tubes offer additional advantages, especially for 2- and 3-wheelers in combination with metallic substrates or as independent systems. Low thermal capacity data indicates an early light off. High thermal conductivity assists the catalyst under engine misfiring conditions. The wall thickness of the foil material used is responsible for low back pressure and high engine performance.The greater geometrical surface area of metallic substrates and hot tubes in combination with structured surfaces offers the automotive industry an opportunity to reduce catalyst volume. Simple, economical canning methods are a field of special interest in the automotive industry. These advantages combined allow metallic substrates a significant market share in automotive applications.For 2- and 3-wheelers, metallic substrates are the first and virtually only choice. The application of hot tubes is recent. It is expected that a large market will arise for hot tubes within the next few years.