Permaculture in New Zealand

Does anyone know anything about rubber carpet underlay in the garden? We've just moved into a house we've had to take the carpet out of as the place stunk, and we have a heap of rubber underlay that must be a great resource for something. I haven't been able to find out how natural the underlay is and whether there would be any issues with using it as mulch on the paths of the vege garden. If anyone has any info or links on this, I'd really appreciate them.

Thanks,

Jo