Difference between Z ultrat and plus?

We have the bright pink Ultrat filament which is not that nice to print with and also the black Ultrat Plus filament on 350g rolls which are removed from the cartridges. It prints beautifully. Is there a difference between the material in the cartridges and the material on the larger rolls? Does the "plus" in the name of the filament refer to the machine it is intended for or is the material different to the Ultrat? Is the black Ultrat going to give the same performance as the Ultrat Plus?

Thank you, Andy.