AkzoNobel 456-21 (21 Series) was a chemically cured two-component, semi-gloss topcoat designed to provide maximum protection from various chemicals, hydraulic fluids, aviation fuels, phosphate ester (Skydrol) fluids and corrosion causing media.

Note: This product is no longer manufactured (although some stock may still be available in certain colours), and AkzoNobel recommend the 456-23 (23 Series) topcoat as an alternative.