Because of the porous structure obtained in commercial sulfuric acid anodizing, the pores require sealing to optimize performance of the layer, including corrosion resistance and dye colour intensity, colour stability and fade resistance. Sealing of anodized layers is simply filling up the pores with some type of larger molecule, and converting the inside of the pore to a hydrated aluminium oxide which closes/plugs the pore.

There are different types of seals that all offer various levels of corrosion performance and dye absorption/stability. ALUMAL Cold Seal technology provides the maximum protection qualities and corrosion resistance for sulfuric anodized coatings. The oxide layer benefits from the sealing process after formation or after colouring. This specific type of hydration of the oxide pores helps with stain and corrosion resistance. Due to higher energy costs of higher temperature sealing, 75-85 OC for mid temperature and 100 OC for traditional hot seals, the cold sealing at room temperature is favoured and allows all the proper chemical reactions to take place for improving anodize layer performance. Sealing at room temperature also helps better stability of colouring or dye processing and offers improved colour fade resistance over conventional high temperature or mid temperature sealing processes.