the reactor these ends are slightly bent away from the strip of material 7 different shapes and configurations of gas outlet nozzles 13 13 a 13 b are also shown in fig5 either the nozzles 13 project slightly above the surface of the gas guide bodies 11 as can be seen in the section of the strip of material 7 c or the nozzles 13 a project beyond the surface of the gas guide bodies 11 a and in addition are bent so that the gas stream leaving the latter first of all strikes the surface of the gas guide bodies 11 a where it is reflected and only thereafter reaches the surface of the strip of material 7 d with a reduced gas pressure and thus in a substantially less turbulent manner if for example as is illustrated with the strip of material 7 b a very small spacing is to be maintained between the gas guide bodies 11 c 11 projecting nozzles would prevent this in this case the nozzles 13 b are therefore sunk within the gas feedlines and distribution devices 12 the nozzles 13 13 a 13 b are preferably slit shaped nozzles that extend over the whole width of the material inlet and outlet openings other shapes of nozzles may however also be employed in many cases the strips of material are bowed because for example they are transported and deflected by rollers that either have a convex or a concave surface fig6 shows an example of strips of material having convexly bowed surfaces the reactor is indicated by the sides of the reactor housing 2 in addition two transporting and reversing rollers 8 together with their shaft butts 16 can be seen the strip of material 7 is bowed.