What is the difference between "unfeasible" and "infeasible"?

Jacking the Link From The Comment (Thanks Josh61), It seems that the words are interchangeable, and it matters not which you choose to use, and is completely down to preference.

One interesting thing to note is that the variant with the "un" prefix was the most common, until the 1970's when the "in" prefix shot past it by a long way. It would be interesting to know the reason for this, but I guess that is a question for another time.

It seems preferable to use infeasible as an adjective, as in, "the infeasibility of the project became apparent", and unfeasible as an adverb, as in, "completion of the project within the timeframe became unfeasible."