Abstract: Composite tube for heating gases to very high temperatures, in particular for generating steam, comprising at least one internal combustion or heating tube (6), an external reinforcement (3) which surrounds the internal tube (6) and spacer means (2,5) for separating the internal tube (6) from the external reinforcement, in which the materials of the internal tube (6) are resistant to the milieus of the heating gases coming into contact with this tube. A jacket tube (1) may be placed between the internal combustion or heating tube (6) and the external reinforcement (3). In the composite tube of this invention the heating tube wall thickness can be reduced and higher temperatures and heat flows can be achieved than hitherto possible.