R 408.13325 Non-rigid helmets.

Rule 3325. A helmet may be made of non-rigid materials where it is to be used in confined spaces, or may be collapsible for convenience in carrying or storing. The helmet may be of the same general shape as a rigid helmet, except that a more complete covering of the top of the head is necessary in order to maintain the face, side, and windows in proper position. The requirements for the filter plates, cover plates, and lens mounting frame are the same as for a rigid helmet. A headgear may be used. The material shall be non-conducting and opaque to ultraviolet, visible, and infrared radiations. Stitched seams shall be welded. Stitching shall not be exposed.