The invention provides a nucleotide sequence representing a pathogenicity island found in species of pathogenic mycobacteria. The improved properties include faster cure, higher maximum torque, higher delta torque, relatively stable modulus over time, improved hot air aging properties and improved aged flexure properties. A characteristic feature also lies in the fact that the wings and are fitted in a linked connection to the sides of the headrest, this latter having a mechanism linking them to each other and locking them thus selectively setting them at a given angle with respect to the headrest.