Stainless steel differs significantly from carbon steel in its composition, structure and properties. As its name suggests, stainless steel is stainless and has superior corrosion resistance when compared with the carbon steel. The most fundamental difference lies in the composition. By definition, steel is considered to be stainless when it contains at least 12% chromium. This is the minimum amount of chromium required in an alloy/steel to maintain its "stainless" surface appearance. The superior corrosion resistance of stainless steel is due to the stability of an ultra thin surface oxide (mainly chromium oxide) - the passive film. If the passive film is broken or damaged due to chemical or mechanical actions, the chromium element in the steel substrate can almost instantly repair the damaged area by re-oxidization (re-passivation). It is this unique self-healing process that makes stainless steel "stainless".

Chromium is the essential element in all types of stainless steels and alloys. Other alloying elements such as nickel and molybdenum are also used to achieve certain required properties. The properties of a stainless steel are determined by it structure which is in turn determined by its alloying composition. There are three types of stainless steels according to the structure: ferritic, austenitic and martensitic. Austenitic grades 304 and 316 are the widely used reinforcing material.

It has long been well established that stainless steels have superior corrosion resistance than carbon steels. Stainless steels and alloys can maintain their natural passivity in seawater or 3.5% NaCl solution. In comparison, the passive behaviour of carbon steel rebars observed in concrete will be totally lost when carbon steels are immersed in seawater or 3.5% NaCl solution, leading to active dissolution and hence continuous loss of material. Research has shown that when the pH of concrete pore water falls below 9, carbon steel rebar will depassivate. Stainless steels can even maintain their passivity in acidic environment. Carbonation and/or chloride ingress would not be able to destroy or depassivate stainless rebars as the chromium oxides (the passive film on stainless steel surface) is much more stable and hence has much greater resistance to corrosion than the iron oxides (the passive film on carbon steel surface). In recent years, more designers and engineers have realised that solid stainless steels offer highest protection against corrosion in concrete structures. With many other alternative CP systems and coated products, the ultimate failure has often been due to over-reliance on that lowest common denominator at construction site level, namely the unskilled labour. This is particularly so for coated/galvanized rebars -which, unlike solid stainless steels, are not homogeneous. Careless handling and installation (cutting, bending) can serously impair their corrosion resistance. With solid stainless steel rebars, however, the integrity and durability will not be affected at all.