Black nozzle filling compound (NFC) is a type of sealing material that is used to fill gaps and spaces between the nozzles and the header plate of a heat exchanger. NFC is typically made from a mixture of epoxy resin, filler materials, and pigments, which provides a strong, durable, and heat-resistant seal. The black color of NFC is typically used in applications where it is necessary to blend in with the surrounding materials, such as in automotive or industrial settings. The compound is applied to the nozzle area and allowed to cure, creating a tight seal that prevents leaks and improves the efficiency of the heat exchanger. NFC is designed to withstand high temperatures and harsh environments, making it ideal for use in applications where heat resistance and durability are critical.