Recycling of rubber offers attractive benefits both in terms of energy conservation and reduction of litter, so it is not surprising that a wide variety of techniques have been investigated from the early part of this century. The cryogenic method, in which vulcanised rubber is taken below its embrittlement temperature and then converted to a powder under high shearing conditions, has been found not only useful for separation of non-rubber components from the rubber, but also for allowing size-reduction of the rubber itself. Despite the fact that cryogenic embrittlement has now been used for almost a decade, there is substantial scope for refining the technique to enable a product with a broader range of end-uses to be manufactured. This paper describes the progress made at the University of New South Wales in relating rubber characteristics (including particle size distribution and surface area) to both grinding conditions and reinforcing performance when used as a filler.