They are made differently but Speedline states only on the larger sizes 17" and 18" which is why I was suprised to read that the Renault 16" are Flowformed. Unless its sourced from a review or magazine that states the Turinis are flowformed just because some of them are......
Description of Flowforming:
The high-tech flow-forming process is based on a different concept to normal casting: starting from a cast flange, with a very thick internal lip (about 3 cm) and a narrow rim width, it is possible to produce a complete wheel through heat spreading material on the rims.
This produces a wheel with extraordinary mechanical characteristics combined with very thin rim thickness, in turn allowing very strong yet lightweight wheels.
A flow-formed rim has an average thickness of 2,7 mm against 4,5 mm of a normal cast wheel: an 18 wheel, for example, represents a weight saving of around one kilo, a great benefit in un-sprung weight reduction.
The flow-formed wheel is lighter than a normal aluminium wheel but also has better mechanical characteristics (resistance, elasticity, longevity): these extraordinary features are obtained by a particularly compact crystalline structure of the metallic alloy, similar in structure to wood fibres.