Abstract: The invention relates to a protective cap for gas container, comprising a cap body forming a protective shell delimiting an internal volume designed to accommodate all or part of the valve-assembly, and an attachment device able to pivot between several angular positions, comprising a rest position in which the attachment device is fully folded, and an attachment position in which the attachment device is completely unfolded. The attachment device comprises a three-dimensional structure comprising two arms each bearing a cutout for fixing to a support, the said three-dimensional structure comprising an interior face shaped to conform to the exterior profile of the body of the cap when the attachment device is in the rest position.