Tanned using aromatic polymers such as the Novolac or Neradol types. This leather is white in color and was invented when vegetable tannins were in short supply, i.e. during the Second World War. Melamine and other amino-functional resins fall into this category as well and they provide the filling that modern leathers often require. Urea-formaldehyde resins were also used in this tanning method until dissatisfaction about the formation of free formaldehyde was realised.