Rotational Moulding is an industrial production technique, used for creating many hollow plastic objects. Marloes ter Bhömer is a Dutch designer based in London, who took this technique to produce this shoe. I guess this is more some sort of conceptual exercise than a real product idea.
You can go and see this project, among many others, at the exhibition Brit Insurance Designs of the Year 2009 at the Design Museum in London till the 14th of June.
This video shows you how the Rotational Moulded Machine tumbles (without a mould though).