Polyimides are lightweight high-performance plastics, flexible and resistant to heat and chemicals, used as mechanical stress buffers, electronic passivation layers, adhesive films in chip bonding, interlayer dielectrics and flexible cables. They are typically spin coated in liquid form, baked and thermally cured between 200 and 400°C. The bake-out removes remaining solvents and the curing anneal creates cross-linking bonds. Low oxygen values are necessary during bake-out and curing to obtain bright, uniformly coloured films with good adhesion.