An elastic retention ring for the combustible casing of a piece of ammunition with respect to a base, the ring including two concentric substantially ring-shaped portions, one internal the other one external. In particular, the invention is concerned with azaindoleoxoacetyl piperazine derivatives. Therefore, the carton comprising said ventilation board when used for fast food packaging provides sufficient ventilation of the carton so that water condensed from food vapors does not run on to the food in the carton, and sufficient insulation so that the food in the carton is kept warm.