They look like one of Sydney's existing Waratah trains, and feel and travel like one.

For passengers, about the only noticeable difference of the 24 new Waratah B-sets from the earlier versions are the orange-coloured exterior of the driver cabins and tweaks to lighting in the carriages and their electronic information displays.

But with surging patronage stretching Sydney's rail network, the new trains will be a welcome relief, especially for commuters in the city's south west.

They have had to endure more than their fair share of uncomfortable trips over summer on old S-sets, dubbed “sweat sets” because of their lack of airconditioning.