OFNP is the outer sheath material of optical cables used in air circulation spaces in buildings (such as ceiling mezzanines, ventilation ducts, etc. It requires the highest flame retardant rating (UL 910/NFPA 262). The following is a cable jacket rating list: OFNP stands for Fiber Optic Non-Conductivity Plenum. To ensure compliance to these requirements, a. What markings should be on the cable for it to be acceptable for use in this application? A: Type OFN cable is listed under the product category for Optical Fiber Cable (QAYK). Cables complying with these requirements are: Type OFNP - Plenum -. Both OFNP and OFNR are fire-rating designations defined by the National Fire Protection Association (NFPA) and are widely used in North America to classify fiber optic cables based on their flame-retardant properties. The nonconductive element within OFNP means they contain no electrically conductive components.