Radiators are made of steel due to the material being of a premium quality, and incorporating a variety of favourable properties.
Stainless steel is renowned for rust-resistance, so can prove a conducive material for durable radiator construction.
Furthermore, stainless steel is a supremely efficient heat conductor, and retains heat very impressively too. Steel radiators can stay warmer for longer as a result, which could positively impact your energy bills.
Also, steel boasts an attractive contemporary look, with the finish also very easy to clean.